Flake8-absolute-import

This is an administrative release, primarily to update officially supported
Python and flake8 versions. There should be no plugin behavior changes between
this version and v1.0.0.1.

Dependencies

- Support for Python 3.12 was officially added

- Support for Python 3.6 and 3.7 was officially removed, though the plugin
should continue to work for Python 3.6+

- The minimum supported flake8 version is now 5.0

Administrative

- `MANIFEST.in` was augmented with the files needed to allow the test suite to
run from an unpacked sdist.

- The build metadata was completely migrated from `setup.cfg` to
`pyproject.toml`, and the maximum possible metadata is now drawn from
`pyproject.toml` (all but `long_description`).

- The read of the project version and the load of the README contents in
`setup.py` was modernized/improved.

Testing

- Python versions in the GitHub Actions and Azure Pipelines matrices were updated.

- An Azure Pipelines job was added to confirm that a built sdist carries all the
files needed to allow the test suite to run.

- Obscure parameters/variables in some tests were given better names, and string
formatting was upgraded to use f-strings.

This is an administrative/metadata release, primarily to update officially
supported Python versions. There should be no behavior changes between
this version and v1.0.0.

Dependencies

- Support for Python 3.10 and 3.11-dev was officially added.

- Support for Python 3.5 was officially removed, though the plugin should remain
compatible.

Testing

- Support for running the `tox` matrix on Windows was removed (it doesn't seem
to work right with the batch-files-in-bin-folder approach I use for multiple
Pythons in development).

- Routine CI was switched from Travis CI to GitHub Actions.

- CI and `tox` versions were updated to focus on Python 3.10.

- `pytest` and `coverage` configs were revised to avoid `source`/`include`
collision in `coverage`.

Administrative

- `setuptools` configuration has been mostly ported to `setup.cfg`, except for the
pieces that still need to be defined dynamically.

- Built artifacts for distribution should now be created using `build`, which
has been added to `requirements-dev.txt`.

Features

- Detect any relative imports and report with error code ABS101.