Added documentation for replacing strings in different files.

Fixes #6

docsrc/search-and-replace.md

@@ -1,13 +1,59 @@
 # Searching and replacing versions
 
-Given this `requirements.txt`:
+Bump-my-version uses [template strings](https://docs.python.org/3/library/string.html#format-string-syntax) to search the configured files for the old or current version and replace the text with the new version.
+
+You can configure the search or replace templates globally and within each `tool.bumpversion.files` entry in your configuration.
+
+The default search template is `{current_version}` to find the version string within the file and replace it with `{new_version}`.
+
+The search and replace templates can be multiple lines, like so:
+
+```toml
+[tool.bumpversion]
+current_version = "1.2.3"
+
+[[tool.bumpversion.files]]
+filename = "config.ini"
+search = "[myproject]\nversion={current_version}"
+replace = "[myproject]\nversion={new_version}"
+```
+
+Alternatively, using [TOML's multiline strings](https://toml.io/en/v1.0.0#string):
+
+```toml
+[tool.bumpversion]
+current_version = "1.2.3"
+
+[[tool.bumpversion.files]]
+filename = "config.ini"
+search = """
+[myproject]
+version={current_version}"""
+
+replace = """
+[myproject]
+version={new_version}"""
+```
+
+## Avoiding incorrect replacements
+
+In files that have multiple version strings, bump-my-version may find the wrong string and replace it. Given this `requirements.txt` for `MyProject`:
 
 ```text
 Django>=1.5.6,<1.6
 MyProject==1.5.6
 ```
 
-using this `.bumpversion.toml` will ensure only the line containing `MyProject` will be changed:
+The default search and replace templates will replace the wrong text. Instead of changing `MyProject`'s version from `1.5.6` to `1.6.0`, it changes `Django`'s version:
+
+```text
+Django>=1.6.0,<1.6
+MyProject==1.5.6
+```
+
+Providing search and replace templates for the `requirements.txt` file will avoid this.
+
+This `.bumpversion.toml` will ensure only the line containing `MyProject` will be changed:
 
 ```toml
 [tool.bumpversion]
@@ -19,7 +65,7 @@ search = "MyProject=={current_version}"
 replace = "MyProject=={new_version}"
 ```
 
-It can be multiple lines, templated using [Python Format String Syntax](https://docs.python.org/3/library/string.html#format-string-syntax).
+
 
 If the string to be replaced includes literal quotes, the search and replace patterns must include them to match. Given the file `version.sh`:
 
@@ -34,49 +80,72 @@ search = "MY_VERSION=\"{current_version}\""
 replace = "MY_VERSION=\"{new_version}\""
 ```
 
----
+## Custom version formats in different files
+
+You can use file configurations to replace the version in multiple files, even if each file has the version formatted differently.
+
+In a module-aware Go project, when you create a major version of your module beyond `v1`, your module name must include the major version number (e.g., `github.com/myorg/myproject/v2`). However, you also have the full version in a YAML file named `release-channels.yaml`.
+
+`go.mod` file:
 
-## Using bumpversion to maintain a go mod file within a Go project
+```go
+module github.com/myorg/myproject/v2
+
+go 1.12
+
+require (
+    ...
+)
+```
 
-In a module-aware Go project, when you create a major version of your module beyond v1, your module name will need to include the major version number (e.g., `github.com/myorg/myproject/v2`).
+`release-channels.yaml` file:
+
+```yaml
+stable: "v2.21.4"
+```
 
 You can use bump-my-version to maintain the major version number within the `go.mod` file by using the `parse` and `serialize` options, as in this example:
 
-- Example `.bumpversion.toml` file:
+ `.bumpversion.toml` file:
 
 ```toml
 [tool.bumpversion]
-current_version = 2.0.0
-commit = True
+current_version = 2.21.4
 
 [[tool.bumpversion.files]]
 filename = "go.mod"
 parse = "(?P<major>\\d+)"
 serialize = "{major}"
 search = "module github.com/myorg/myproject/v{current_version}"
 replace = "module github.com/myorg/myproject/v{new_version}"
+
+[[tool.bumpversion.files]]
+filename = "release-channels.yaml"
 ```
 
-- Example `go.mod` file:
+While all the version bumps are `minor` or `patch`, the `go.mod` file doesn't change, while the `release-channels.yaml` file will. As soon as you do a `major` version bump, the `go.mod` file now contains this module directive:
 
 ```go
-module github.com/myorg/myproject/v2
+module github.com/myorg/myproject/v3
+```
 
-go 1.12
+## Multiple replacements within the same file
 
-require (
-    ...
-)
-```
+To make several replacements in the same file, you must configure multiple `[[tool.bumpversion.files]]` sections for the same file with different configuration options.
 
-Then run this command to create version 3.0.0 of your project:
+In this example, the changelog is generated before the version bump. It uses `Unreleased` as the heading and includes a link to GitHub to compare this version (`HEAD`) with the previous version.
 
-```console
-bump-my-version --new-version 3.0.0 major
-```
+To change `Unreleased ` to the current version, we have an entry with `search` set to `Unreleased`.  The default `replace` value is `{new_version}`, so changing it is unnecessary.
 
-Your `go.mod` file now contains this module directive:
+To change the link, another entry has its `search` set to `{current_version}...HEAD` and the `replace` set to `{current_version}...{new_version}`.
 
-```go
-module github.com/myorg/myproject/v3
+```toml
+[[tool.bumpversion.files]]
+filename = "CHANGELOG.md"
+search = "Unreleased"
+
+[[tool.bumpversion.files]]
+filename = "CHANGELOG.md"
+search = "{current_version}...HEAD"
+replace = "{current_version}...{new_version}"
 ```