Merge configurations into pyproject.toml

[fwitte]

Resolve #1072
Resolve #712

[fwitte]

@oemof-developer: I think this should be ready for review. There are two remaining questions:

• Is anybody knowledgeable if pydocstyle actually does anything?
• The black error is in some source files I never touched, should that be fixed or not?

Quick explanation/overview of the changes:

• setup.cfg (deleted)
  • flake8 related stuff moved to new file: .flake8
  • pep257 deleted, seems to be the same as pydocstyle
  • everything else moved to pyproject.toml
• setup.py, MANIFEST.in (all deleted)
  • completely migrated to pyproject.toml
• .prospector (deleted)
  • same as pydocstyle and pep257, does not seem to affect any test

[fwitte]

One more comment to the build system: I changed from setuptools to flit, because setuptools based on pyproject.toml did not support pip install -e last time I checked, and also because I am using it in other tools, where I migrated to pyproject.toml, e.g. tespy.

I am very open to discuss this btw. because I am by no means an expert in this, according to this post, it seems setuptools should provide editable installation for pure pyproject.toml as well: https://stackoverflow.com/questions/69711606/how-to-install-a-package-using-pip-in-editable-mode-with-pyproject-toml

[p-snft]

First of all, you questions:

Is anybody knowledgeable if pydocstyle actually does anything?

I don't but I think this is nothing to be fixed here. If it does not do anything, it should be removed independend from the switch to pyproject.toml.

The black error is in some source files I never touched, should that be fixed or not?

This is an unrelated problem, as it should have been wrong before you changed things. So, it should not be included in this merge request.

The same is true for the last comment I gave. Making support for Python 3.11 (which is tested) official might be something for a separate merge.

PS: I was a bit surprised that https://github.com/oemof/oemof/wiki/How-to-release still works exactly the same way as before.

[fwitte]

One more question, what is the VERSION file for?

VERSION was deleted, also see #712