Migrate project metadata to `pyproject.toml` (PEP 621)

Hi there,

this is my first issue here.

I saw that your project has both a `setup.py` and a `pyproject.toml`. Most of the project metadata can be migrated to the toml file. Would you like a PR for that migration or do you prefer staying with `setup.py`?

Ref: https://peps.python.org/pep-0621/