Add mdbook based user guide (#658)

* Add mdbook based user guide

* Add netlify config file

* Update guide/src/installation.md

Co-authored-by: David Hewitt <1939362+davidhewitt@users.noreply.github.com>

* Update installation guide

* Update bindings guide

* Update metadata guide

* Add tutorial first draft.

* Add project layout draft.

* Correct informaton about Python type hints in project layout guide.

* Add bindings section draft.

* Update guide/src/bindings.md

* Upgrade mdbook to 0.4.13

* Add repository metadata to mdbook configuration

Co-authored-by: David Hewitt <1939362+davidhewitt@users.noreply.github.com>
Co-authored-by: Ashley Anderson <aanderson@hyperfine-research.com>

guide/.gitignore

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+book

guide/book.toml

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+[book]
+author = ["PyO3 Project and Contributors"]
+language = "en"
+multilingual = false
+src = "src"
+title = "Maturin User Guide"
+
+[output.html]
+git-repository-url = "https://github.com/PyO3/maturin/tree/main/guide"
+edit-url-template = "https://github.com/PyO3/maturin/edit/main/guide/{path}"

guide/src/SUMMARY.md

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+# Summary
+
+[Introduction](index.md)
+
+---
+
+- [Installation](./installation.md)
+- [Tutorial](./tutorial.md)
+- [Project Layout](./project_layout.md)
+- [Bindings](./bindings.md)
+- [Python Metadata](./metadata.md)
+- [Local Development](./develop.md)
+- [Distribution](./distribution.md)

guide/src/bindings.md

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+# Bindings
+
+Maturin supports several kinds of bindings, some of which are automatically
+detected. You can also pass `-b` / `--bindings` command line option to manually
+specify which bindings to use.
+
+## `pyo3`
+
+[pyo3](https://github.com/PyO3/pyo3) is Rust bindings for Python,
+including tools for creating native Python extension modules.
+It supports both CPython and PyPy.
+
+maturin automatically detects pyo3 bindings when it's added as a dependency in `Cargo.toml`.
+
+### `Py_LIMITED_API`/abi3
+
+pyo3 bindings has `Py_LIMITED_API`/abi3 support, enable the `abi3` feature of the `pyo3` crate to use it:
+
+```toml
+pyo3 = { version = "0.14", features = ["abi3"] }
+```
+
+You may additionally specify a minimum Python version by using the `abi3-pyXX`
+format for the pyo3 features, where `XX` is corresponds to a Python verison.
+For example `abi3-py37` will indicate a minimum Python version of 3.7.
+
+> **Note**: Read more about abi3 support in [pyo3's
+> documentation](https://pyo3.rs/latest/building_and_distribution.html#py_limited_apiabi3).
+
+### Cross Compiling
+
+pyo3 bindings has decent cross compilation support.
+For manylinux support the [manylinux-cross](https://github.com/messense/manylinux-cross) docker images can be used.
+
+> **Note**: Read more about cross compiling in [pyo3's
+> documentation](https://pyo3.rs/latest/building_and_distribution.html#cross-compiling).
+
+## `cffi`
+
+Cffi wheels are compatible with all python versions including pypy. If `cffi`
+isn't installed and python is running inside a virtualenv, maturin will install
+it, otherwise you have to install it yourself (`pip install cffi`).
+
+Maturin uses cbindgen to generate a header file for [supported Rust
+types](https://github.com/eqrion/cbindgen/blob/master/docs.md#supported-types).
+The header file can be customized by configuring cbindgen through a
+`cbindgen.toml` file inside your project root. Aternatively you can use a build
+script that writes a header file to `$PROJECT_ROOT/target/header.h`, like so:
+
+```rust
+use cbindgen;
+use std::env;
+use std::path::Path;
+
+fn main() {
+    let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
+
+    let bindings = cbindgen::Builder::new()
+        .with_no_includes()
+        .with_language(cbindgen::Language::C)
+        .with_crate(crate_dir)
+        .generate()
+        .unwrap();
+    bindings.write_to_file(Path::new("target").join("header.h"));
+}
+```
+
+Maturin uses the cbindgen-generated header to create a module that exposes `ffi` and
+`lib` objects as attributes. See the [cffi docs](https://cffi.readthedocs.io/en/latest/using.html)
+for more information on using theses `ffi`/`lib` objects to call the Rust code
+from Python.
+
+> **Note**: Maturin _does not_ automatically detect `cffi` bindings. You _must_
+> specify them via either command line with `-b cffi` or in `pyproject.toml`.
+
+## `rust-cpython`
+
+[rust-cpython](https://github.com/dgrunwald/rust-cpython) is Rust bindings for
+the Python interperter. Currently it only supports CPython.
+
+Maturin automatically detects rust-cpython bindings when it's added as a
+dependency in `Cargo.toml`.
+
+## `bin`
+
+Maturin also supports distributing binary applications written in Rust as
+Python packages using the `bin` bindings. Binaries are packaged into the wheel
+as "scripts" and are available on the user's `PATH` (e.g. in the `bin`
+directory of a virtual environment) once installed.
+
+> **Note**: Maturin _does not_ automatically detect `bin` bindings. You _must_
+> specify them via either command line with `-b bin` or in `pyproject.toml`.

guide/src/develop.md

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+# Local Development
+
+TODO

guide/src/distribution.md

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+# Distribution
+
+## Source Distribution
+
+TODO
+
+## Build Wheels
+
+TODO

guide/src/index.md

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+# Maturin User Guide
+
+Welcome to the maturin user guide! It contains examples and documentation to explain all of maturin's use cases in detail.
+
+Please choose from the chapters on the left to jump to individual topics, or continue below to start with maturin's README.
+
+{{#include ../../Readme.md}}

guide/src/installation.md

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+# Installation
+
+## Install from package managers
+
+### PyPI
+
+maturin is published as Python binary wheel to PyPI, you can install it using pip:
+
+```bash
+pip install maturin
+```
+
+### Homebrew
+
+On macOS [maturin is in Homebrew](https://formulae.brew.sh/formula/maturin#default) and you can install maturin from Homebrew:
+
+```bash
+brew install maturin
+```
+
+### conda
+
+Installing from the `conda-forge` channel can be achieved by adding `conda-forge` to your conda channels with:
+
+```
+conda config --add channels conda-forge
+conda config --set channel_priority strict
+```
+
+Once the `conda-forge` channel has been enabled, `maturin` can be installed with:
+
+```
+conda install maturin
+```
+
+### Alpine Linux
+
+On Alpine Linux, [maturin is in community repository](https://pkgs.alpinelinux.org/packages?name=maturin&branch=edge&repo=community)
+and can be installed with `apk` after [enabling the community repository](https://wiki.alpinelinux.org/wiki/Enable_Community_Repository):
+
+```bash
+apk add maturin
+```
+
+## Download from GitHub Releases
+
+You can download precompiled maturin binaries from the latest [GitHub Releases](https://github.com/PyO3/maturin/releases/latest).
+
+## Build from source
+
+### crates.io
+
+You can install maturin from [crates.io](https://crates.io/crates/maturin) using cargo:
+
+```bash
+cargo install maturin
+```
+
+### Git repository
+
+```bash
+cargo install --git https://github.com/PyO3/maturin.git maturin
+```

guide/src/metadata.md

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+# Python Project Metadata
+
+maturin supports [PEP 621](https://www.python.org/dev/peps/pep-0621/),
+you can specify python package metadata in `pyproject.toml`.
+maturin merges metadata from `Cargo.toml` and `pyproject.toml`, `pyproject.toml` take precedence over `Cargo.toml`.
+
+## Add Python dependencies
+
+To specify python dependencies, add a list `dependencies` in a `[project]` section in the `pyproject.toml`. This list is equivalent to `install_requires` in setuptools:
+
+```toml
+[project]
+dependencies = ["flask~=1.1.0", "toml==0.10.0"]
+```
+
+## Add console scripts
+
+Pip allows adding so called console scripts, which are shell commands that execute some function in you program. You can add console scripts in a section `[project.scripts]`.
+The keys are the script names while the values are the path to the function in the format `some.module.path:class.function`, where the `class` part is optional. The function is called with no arguments. Example:
+
+```toml
+[project.scripts]
+get_42 = "my_project:DummyClass.get_42"
+```
+
+## Add trove classifiers
+
+You can also specify [trove classifiers](https://pypi.org/classifiers/) in your Cargo.toml under `project.classifiers`:
+
+```toml
+[project]
+classifiers = ["Programming Language :: Python"]
+```

guide/src/project_layout.md

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+# Project Layout
+
+Maturin expects a particular project layout depending on the contents of the
+package.
+
+## Pure Rust project
+
+For a pure Rust project, the structure is as expected and what you get from `cargo new`:
+
+```
+my-rust-project/
+├── Cargo.toml
+├── pyproject.toml  # required for maturin configuration
+└── src
+    ├── lib.rs  # default for library crates
+    └── main.rs  # default for binary crates
+```
+
+Maturin will add a necessary `__init__.py` to the package when building the
+wheel. For convenience, this file includes the following:
+
+```python
+from .my_project import *
+
+__doc__ = .my_project.__doc__
+```
+
+such that the module functions may be called directly with:
+
+```python
+import my_project
+my_project.foo()
+```
+
+rather than:
+
+```python
+from my_project import my_project
+```
+
+> **Note**: there is currently no way to tell maturin to include extra data (e.g.
+`package_data` in setuptools) for a pure Rust project. Instead, consider using
+the layout described below for the mixed Rust/Python project.
+
+## Mixed Rust/Python project
+
+To create a mixed Rust/Python project, add a directory with your package name
+(i.e. matching `lib.name` in your `Cargo.toml`) to contain the Python source:
+
+```
+my-rust-and-python-project
+├── Cargo.toml
+├── my_project  # <<< add this directory and put Python code in here
+│   ├── __init__.py
+│   └── bar.py
+├── pyproject.toml
+├── Readme.md
+└── src
+    └── lib.rs
+```
+
+Note that in a mixed Rust/Python project, maturin _does not_ modify the
+existing `__init__.py` in the root package, so now to import the rust module in
+Python you must use:
+
+```python
+from my_project import my_project
+```
+
+You can modify `__init__.py` yourself (see above) if you would like to import
+functions Rust functions from a higher-level namespace.
+
+### Alternate Python source directory (src layout)
+
+Having a directory with `package_name` in the root of the project can
+occasionally cause confusion as Python allows importing local packages and
+modules. A popular way to avoid this is with the `src`-layout, where the Python
+package is nested within a `src` directory. Unfortunately this interferes with
+the structure of a typical Rust project. Fortunately, Python is nor particular
+about the name of the parent source directory. You tell maturin to use a
+different Python source directory in `Cargo.toml` by setting
+`package.metadata.maturin.python-source`. For example:
+
+```toml
+[package.metadata.maturin]
+python-source = "python"
+```
+
+then the project structure would look like this:
+
+```
+my-rust-and-python-project
+├── Cargo.toml
+├── python
+│   └── my_project
+│       ├── __init__.py
+│       └── bar.py
+├── pyproject.toml
+├── README.md
+└── src
+    └── lib.rs
+```
+
+## Adding Python type information
+
+To distribute typing information, you need to add:
+
+* an empty marker file called `py.typed` in the root of the Python package
+* inline types in Python files and/or `.pyi` "stub" files
+
+In a pure Rust project, add type stubs in a `<module_name>.pyi` file in the
+project root. Maturin will automatically include this file along with the
+required `py.typed` file for you.
+
+```
+my-rust-project/
+├── Cargo.toml
+├── my_project.pyi  # <<< add type stubs for Rust functions in the my_project module here
+├── pyproject.toml
+└── src
+    └── lib.rs
+```
+
+In a mixed Rust/Python project, additional files in the Python source dir (but
+not in `.gitignore`) will be automatically included in the build outputs
+(source distribution and/or wheel). Type information can be therefore added to
+the root Python package directory as you might do in a pure Python package.
+This requires you to add the `py.typed` marker file yourself.
+
+```
+my-project
+├── Cargo.toml
+├── python
+│   └── my_project
+│       ├── __init__.py
+│       ├── py.typed  # <<< add this empty file
+│       ├── my_project.pyi  # <<< add type stubs for Rust functions in the my_project module here
+│       ├── bar.pyi  # <<< add type stubs for bar.py here OR type bar.py inline
+│       └── bar.py
+├── pyproject.toml
+├── README.md
+└── src
+    └── lib.rs
+```