Flasksimpleauth

- major code refactoring to break the monolith `FlaskSimpleAuth` class
- add custom authentication scheme
- use sphinx to generate doc with new pipeline
- add automatic API doc

- fix minor issues
- improved documentation

- add `Header` and `Cookie` special parameters.
- various test fixes.

News:
- switch to `pyproject.toml`
- drop support for Python 3.7, 3.8 and 3.9.
- improve tests
- add support for implementing multi-factor authentication

- Add a minimal `pyproject.toml`: yet another useless file, which would be a good thing if it *replaced* other files, alas the two `setup.*` files are still required.
- Add support for data classes and [pydantic](https://pydantic.dev/) classes as parameter types.
- Add an after auth/before exec hook, executed just before actually calling the route function.
- Report all possible *400* instead of stopping on the first issue.
- Improve documentation.

- fix badly thought attempt at upward compatibility.
**WHAT IS NOT TESTED DOES NOT WORK!**