move project metadata to pyproject.toml

[ThomasWaldmann]

also: replace flake8 by ruff.

[ThomasWaldmann]

I converted the metadata from setup.cfg "as is" to pyproject.toml.
I also added some stuff that is currently commented out as a suggestion, these were not present in setup.cfg.

Maybe interesting for another PR: https://stackoverflow.com/questions/74608905/single-source-of-truth-for-python-project-version-in-presence-of-pyproject-toml

[ThomasWaldmann]

Hmm, the black section targets py37 (which is not within the supported python versions) - shall that be py38?

[ThomasWaldmann]

@methane Maybe you missed my comment about the suggestions / commented stuff in pyproject.toml - maybe just look through it and remove the comment chars to activate all suggestions you like to have.