Change docstring style to numpydocs

[Opt-Mucca]

What was done in this MR:

• Unified docstring style to numpydoc
• Added missing information on parameters to docstring where appropriate
• Add new style of showing the API to the online documentation.

What I did not do:

• Change the docstrings of all tests + other pieces of code. I think much of this will come from implementing a style formatter.
• I did not add type hints. If anything I removed the few that we had. Guides online suggest that they are redundant if the docstrings are done properly. IDEs should now be able to extract the types for all parameters for instance. Implementing type hints in Cython is also different than standard Python. For instance, mypy requires an additional file with each function declaration.

[Opt-Mucca]

@Joao-Dionisio I didn't expect such a robust review. So I'm not sure if I even spent that much more time comparatively. All the changes should be addressed now! Thank you for fixing a lot of the small errors.