split ci into stages
Related to the remaining action points in #13 (closed)
Summary of changes:
- Add a test for trailing whitespace
- Add a test for broken URLs in docs, fix all broken URLs and permanent redirects
- Switch sphinx doc build to strict (warnings to errors) and nitpicky (broken links to warnings). Fix all sphinx warnings.
- Deploy docs from any commit to kwant/kwant to https://test.kwant-project.org/doc/dev
- Deploy docs from any commit to master at kwant/kwant to https://kwant-project.org/doc/dev
- Deploy docs from any tag release tag (so anything that is vX.Y.Z) at kwant/kwant to https://kwant-project.org/doc/X.Y