setup.py is dead, long live pyproject.toml

[drbenvincent]

Closes #105. This PR greatly simplifies things. We've moved to a more modern workflow where all the config stuff is contained in pyproject.toml.

So I've been able to delete:

• setup.py
• .isort.cfg
• manifest.in
• requirements.txt
• requirements-dev.txt
• requirements-docs.txt
• requirements-lint.txt
• requirements-test.txt

The requirements are now in pyproject.toml. Devs can install by running pip install causalpy[dev] for example.

Instructions to developers have been updated in CONTRIBUTING.md

Tests pass locally and remotely.

I've been through a build, upload to pypi, install process and can confirm it's pip installable in a temp local environment.

Oh, and the dev environment now uses pymc>=5.0.0 🎉

PS. When I was testing, I uploaded to pypi with version 0.0.10a, thinking that is counted as a pre-release. But I think it's the case that anyone doing pip install causalpy will already be getting this version not yet merged into main.

Remaining things

• The only downside to the current situation is that the version number is in two places. But this may be fixable with try to get dynamic version in pyproject.toml #155. If not, it will be easy if we use some auto version bump tool. Otherwise manual is fine for the moment.
• setup.cfg remains now because flake8 doesn't play ball with pyproject.toml. There may be something we can do about this in the future.

[juanitorduz]

great!