Pip-check-reqs

- Performance improvements.
- Add preliminary support for Windows.

- Fix an issue with importing `__main__`.
- Fix an issue with importing packages with periods in their names.

- Support Python 3.10.
- Remove support for Python 3.8.
- Bump `pip` requirement to 23.2.

- Bump `packaging` requirement to >= 20.5. Older versions of `pip-check-reqs` may be broken with the previously-specified version requirements.

- Improves performance on Python 3.11.

- Added support for Python 3.11.
- Added `python_requires` to metadata; from now on, releases of
`pip-check-reqs` are marked as compatible with Python 3.8.0 and up.
- Made `--version` flag show interpretter version and path to the package which
pip-check-reqs is running from, similar to information shown by `pip
--version`.
- `-V` is now an alias of `--version`.