Migrate from setup.cfg to pyproject.toml for project metadata

This is the latest standard way to specify project metadata, as per PEP 621
Also move flake8 config back tox.ini
This means we can have one less file in the repo root.

setuptools + pyproject.toml automatically supports "src-layout" projects,
so will automatically find the source code in "src" directory.

pyproject.toml

@@ -2,6 +2,51 @@
 requires = ["setuptools ~= 68.0"]
 build-backend = "setuptools.build_meta"
 
+[project]
+name = "django-dirtyfields"
+dynamic = ["version"]
+description = "Tracking dirty fields on a Django model instance."
+keywords = ["django", "dirtyfields", "track", "model", "changes"]
+readme = "README.rst"
+license = {file = "LICENSE"}
+authors = [{name = "Romain Garrigues"}]
+maintainers = [{name = "Lincoln Puzey"}]
+requires-python = ">=3.8"
+dependencies = [
+  "Django>=2.2",
+]
+classifiers = [
+    "Development Status :: 5 - Production/Stable",
+    "Intended Audience :: Developers",
+    "Topic :: Software Development :: Libraries :: Python Modules",
+    "License :: OSI Approved :: BSD License",
+    "Natural Language :: English",
+    "Operating System :: OS Independent",
+    "Programming Language :: Python",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3 :: Only",
+    "Programming Language :: Python :: 3.8",
+    "Programming Language :: Python :: 3.9",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Framework :: Django",
+    "Framework :: Django :: 2.2",
+    "Framework :: Django :: 3.0",
+    "Framework :: Django :: 3.1",
+    "Framework :: Django :: 3.2",
+    "Framework :: Django :: 4.0",
+    "Framework :: Django :: 4.1",
+    "Framework :: Django :: 4.2",
+]
+
+[project.urls]
+Homepage = "https://github.com/romgar/django-dirtyfields"
+Changelog = "https://github.com/romgar/django-dirtyfields/blob/develop/ChangeLog.rst"
+Documentation = "https://django-dirtyfields.readthedocs.io"
+
+[tool.setuptools.dynamic]
+version = {attr = "dirtyfields.__version__"}
+
 [tool.pytest.ini_options]
 django_find_project = false
 DJANGO_SETTINGS_MODULE = 'tests.django_settings'

tox.ini

@@ -35,3 +35,8 @@ commands =
     python --version
     pip list
     flake8 -v src tests docs
+
+[flake8]
+ignore = E133,W503
+max-line-length = 120
+extend-exclude = docs/_build,docs/.venv-docs