Migrating setup.py and setup.cfg to UV package manager and Travis to GitHub Actions

[ok-lch]

Hello @schymans 😄

Here is some changes that can give a good start to help fixing #91.
Its not perfect yet but I think its a good start.

I have change the dependencies management system to use uv, moving from setup.py and setup.cfg files to a pyproject.toml file.

I removed Travis pipeline to use GitHub Actions.
Tests are running and passing for python version 3.8 and 3.9.
There is still two jobs that need some tinkering (publishing the documentation and the package).

I haven't done many upgrades on dependencies.
Only one fix regarding pkg_resources in _generator.py

I have put some documentation in the CONTRIBUTING.md file but I think it may not be the right place as I have seen later that there it should fit better in docs/installation.rst in the Development section.

Kind regards,
Laurent

[schymans]

This is amazing work, thank you! I had trouble running the tests at first and left a comment in the file contributing.md where you described what to do. Perhaps this could be clarified before merging? I also had some warnings when building the docs, did you see these, too?

[schymans]

I have only been able to successfully run the tests after running uv sync --all-groups . uv sync --group tests was also sufficient to run the tests, but they failed because of the missing yapf, whereas uv sync --group generator somehow uninstalled pytest again, so couldn't run tests any more. Perhaps I am misunderstanding uv, but others might have the same problem.