Add a minimal pyproject.toml for PEP517

[afg1]

This PR allows pip isolated builds to work, but still uses the same build infrastructure as always, so shouldn't break anything.

I needed this because I develop a pipeline running on python 3.11, for which there isn't a wheel yet. The dependency manager I'm using (poetry) does all its builds in isolated environments, which is fine when setup.py doesn't depend on anything except setuptools and/or wheel but has problems when you need e.g. cython

The solution is to add a minimal pyproject.toml file that includes the build dependencies, and specifies the correct build backend. That way, the isolated enviroment used for the build ends up with Cython, and everyone is happy.

I added some stuff to the project description, but this is all already in setup.cfg I think, so could be removed. Ideally, everything would end up in the pyproject.toml but I didn't want to break anything since I'm not 100% sure how this all interacts with e.g. CI and pushing to PyPI.

[sinoroc]

Related:

• https://stackoverflow.com/q/75372835

[sinoroc]

@afg1 For a first step, you should have only the [build-system] section, but without the :__legacy__ part which seems unnecessary. https://setuptools.pypa.io/en/latest/userguide/pyproject_config.html