Docs/multiversion migration

[mschmidt87]

This PR migrates our docs from github pages to readthedocs. It also features multiversion and will currently host two versions:

• latest (master branch)
• 0.2.0 (this is actually not build from the 0.2.0 tag because this version does not have a config file for readthedocs, but from the 0.2.0_rtd branch which branches off from 0.2.0 and has the config file, therefore it is displayed as 0.2.0_rtd in the pulldown menu in the documentation)

This PR

• deletes the deploy_docs.yaml config file for github actions
• changes the docs banner link in the README
• changes the version to 0.3.0.dev0

You can view the docs here: https://hal-cgp.readthedocs.io/en/latest/

Closes #251

[HenrikMettler]

Thanks a lot for taking care of this :) Lgtm

[jakobj]

thanks a lot, looks good! 🚀

one badge is not rendered properly for me on readthedocs, do you seen the same issue? i think it's the mypy badge.

[HenrikMettler]

thanks a lot, looks good! rocket

one badge is not rendered properly for me on readthedocs, do you seen the same issue? i think it's the mypy badge.

No everything looks fine for me...