PEP 621 compatibility

With the introduction of PEP 621, setup.py is deprecated.
Setuptools describes it here:

Starting with PEP 621, the Python community selected pyproject.toml as a standard way of specifying project metadata. Setuptools has adopted this standard and will use the information contained in this file as an input in the build process.

Let's see if we can update our project, especially because we've a dynamic file list.