Add return sections to the docstrings #76
Description
Copied from PsiQ/bartiq #77
As @dexter2206 pointed out in PsiQ#76, we lack return statements in some public methods.
It's not a big problem when reading the docstrings, but if the return statements are there, it renders much more nicely on the website docs.
This issue is about reviewing the docstrings of all the public methods and adding return statements wherever they're missing.