Docstrings standardization

[FBruzzesi]

Description

This PR aims to refactor all the modules docstring in order to standardize them into numpy style.
Therefore numpydoc dependency and extension has been added as well.

Remark: The target building tool is mkdocs-materials instead of sphinx, therefore some part will not render properly when tested with sphinx. If the decision is to stick with sphinx, then more changes are necessary.

To check how those would render, I added a minimal (?) mkdocs.yaml which reads mkdocs/ folder containing just a page API rendering.

It can be tested by running the following command:

python -m pip install \
    mkdocs==1.5.3 \
    mkdocs-autorefs==0.5.0 \
    mkdocs-material==9.4.5 \
    mkdocs-material-extensions==1.2 \
    mkdocstrings==0.23.0 \
    mkdocstrings-python==1.7.3 
mkdocs serve

Additional information

• I tried to keep the original docstrings as much as possible
• In some classes there are example usage but not nearly in the most of them. It would be good for future to add a simple example for each class
• All code changes are solely due to black and isort with line length of 120

[koaning]

Spotted a table rendering issue.

[koaning]

params also don't render super well on this one

[FBruzzesi]

• For the table, the best solution I found is to make it in code as
  
  Since the table concept is slightly different in mkdocs.
• Thanks for the heads up on the parameters, the ":" at the end has been wrongly copy-pasted in a few places

[koaning]

Great job! I only found one page with issues here. That's a ton of work!

I left one comment about adding the import path. I don't know if it can be automated. But it might be nice to perhaps manually add on top?

[koaning]

I couldn't find any more issues from eyeballing this ... so I think it's good to merge :)