Modern setup configuration

[videlec]

Python packaging is shifting toward havin a pyproject.toml at the root of the package that specifies the tool to install the package (for this package this would be setuptools). Also it becomes more common to specify the setup options in a setup.cfg file rather than in the setup.py. This way of doing is much more complete to specify build dependencies and runtime dependencies.

Part of openjournals/joss-reviews#3996

[fredstro]

I have removed everything I can from the setup.py and put into the pyproject.toml and setup.cfg.
As far as I can tell the Cython extension modules still need to be in setup.py

[fredstro]

This is done.