Suggest to use common docstring format for primitives

I would suggest numpy docstring style:

• https://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_numpy.html
• https://numpydoc.readthedocs.io/en/latest/

This style is used by Numpy and Sklearn, among others, so I think it is reasonable that we also use it.

Currently it is already used by AbstractMetaclass, which if you use it in your class (already used by primitive base class) automatically ineherits docstrings and merges them with parent parameter documentation if only description is provided, for numpy style. Read more here.