Add support for Python 3.11, drop EOL 3.6-3.7

[hugovk]

https://devguide.python.org/versions/

[hugovk]

Actually, this overlaps a lot with #79, let's update that one instead.

[radarhere]

Ok, i've updated #79 with these changes - except for allow-prereleases: true. From what I see, that doesn't have any effect with the current configuration.

[hugovk]

Ok, i've updated #79 with these changes - except for allow-prereleases: true. From what I see, that doesn't have any effect with the current configuration.

Yep, it's not needed yet. I meant to leave that out, it was from trying to add 3.12, but that needs the setup.py upgrading not to expect the removed setuptools. A pyproject.toml with a defined build backend should do it, but it can wait for later.