Jazzband guidelines

[piyueh]

This PR should resolve the following tasks in #13:

• [x] Fix all links in the docs (and README file etc) from old to new repo
• [x] Add the Jazzband badge to the README file
• [x] Add the Jazzband contributing guideline to the CONTRIBUTING.md or CONTRIBUTING.rst file
• [x] Port tests to GitHub Actions (if not already there)
• [x] Check if test coverage services work (e.g. Coveralls, Codecov, etc)
• [x] Set up CI for Jazzband project releases if needed ~and open ticket if yes~

The PR only partially resolves the auto-release workflow of GitHub Actions. I added a hook/workflow to integrate the PyPI releasing and GitHub Actions. However, an issue has to be open at https://jazzband.co/roadies/issue to notify the Jazzband roadies. That says, once merged, we need to add the following new task to #13:

• open an issue at https://jazzband.co/roadies/issue to enable auto-release to PyPi

[piyueh]

@graingert Would you like to review/merge this PR?

[piyueh]

@graingert I updated them based on the suggestions in commit 34898462be068fd93710ec5b037027ab486494f5. In addition,

1. I moved the content of tox.ini to pyproject.toml to have fewer configuration files.
2. tox now by default only runs regular tests. Users have to provide CMD argument --cov to tox if they want to do coverage tests (as shown in test.yml).

Thanks for the suggestions! I learned a lot of new things.

[jezdez]

Hey all, I noticed this is using Coveralls, could you please use Codecov instead to reduce the number of services?