project layout

[nim65s]

I still need to add :

• [x] mock code with internal imports
• [x] unittests
• [x] doctests

I hope to finish that Tomorrow.

After this is merged, I'll also have to setup external stuff for

• [x] pre-commit.ci
• [ ] codecov
• [x] read the docs

[nim65s]

This is now good for me.

We'll probably want to discuss more about authors / maintainers here, in pyproject.toml & CITATION.cff.

@ElliotMaitre : I'll let you take a look at this now :)

[ElliotMaitre]

Thanks ! It looks good to me, we can now start moving files around to fit to this new layout.