https://pip.pypa.io/en/stable/reference/build-system/pyproject-toml/

An initial pyproject.toml is being added with only mypy for starters in #1179. This would entail creating [project] and removing setup.py entirely. It will work on all Python versions as long as the pip is sufficiently new enough, and it is in our 3.7 CI image (https://github.com/shivupa/cclib-ci/blob/2f8301d98a3a54d1a8cc7e97523fa34d1efc394c/py37/environment.yml#L203).

Reminder to not let #833 get left behind.