Add a pyproject.toml

[kpcyrd]

This allows building the project into a wheel with:

python -m build --wheel --no-isolation

Instead of the deprecated:

./setup.py build

[Ousret]

Indeed, we'll have to make one.
Unfortunately, I don't want a minimalist one, the plan is to remove setup.cfg and maybe (if possible) setup.py.
The build backend should be hatchling.

If you want to take a shot at this, I'll review it.
Otherwise, I'll do it later.