How to document classes in HySoP

We try to fit as much as possible with numpydoc guide guide standards.

See the files fields/continuous.py and operator/drag_and_lift.py which are used as reference files for documentation.

Mind the need of raw strings litterals in python docstrings for keeping the stuff from math environments “.. :math:”.

Mind the ‘space’ character before colon character “:” in parameters or attributes definitions.

Any code sample in docstring should be written as a doctest code sample (see https://docs.python.org/3/library/doctest.html).