Convert this project from setup.py to pyproject.toml

[john-science]

This project (for the obvious historical reasons) uses setup.py. And I have not been bothered to change that because, "It works, so who cares." But it looks like future versions of Python will really need pyproject.toml, and not setup.py.

• We want to support the pyproject.toml.
• It should be an easy enough change.
• We need to be careful to not drop support for older versions of Python.

[john-science]

I am not sure this is worth doing.

The Python org is pushing so hard for everyone to abandon the old setup.py approach and move to the new pyproject.toml approach. But according to the official setuptools docs, there is no way to build a Cython project with only a pyproject.toml file; you will still need a setup.py file to go with it.

Which begs the question:

Why should I bother moving to an inferior tech that doesn't even support Cython?

Sounds like a waste of time. (See relevant StackOverflow post.)