Declare project and pytest configuration in pyproject.toml

[EpicWink]

Uses PEP 518 and PEP 621. Drops support for Python 3.6 and running tests via python setup.py.

setup.py-less editable installs are blocked by pypa/setuptools#3082 (likely setuptools v64), so a stub setup.py remains.

[codecov[bot]]

Codecov Report

Merging #80 (817921c) into master (c3689c9) will not change coverage. The diff coverage is n/a.

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  Lines         310      310           
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  Hits          263      263           
  Misses         47       47           

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[jenshnielsen]

@EpicWink I believe it would be possible to do the main part of this provided that you leave a stup setup.py file around https://pip.pypa.io/en/stable/reference/build-system/pyproject-toml/?highlight=660#editable-installation even without setuptools supporting pep660. How do you think about that

[Chilipp]

I agree to @jenshnielsen, we should still keep a setup.py file unless you can give me a good reason why it should be removed. What do you think @EpicWink ?

[EpicWink]

Sounds good, I'll get to it tomorrow and test