Improve the docstrings

[maximlt]

I'd like the docstrings of the public API methods and functions of Param to be improved which should improve:

• the API reference page of the website
• the user experience in a code editor

I'm opening this issue to report (later) ideas and findings. For now I would just like to note that Param doesn't seem to follow PEP257 and also doesn't follow any format (presumably because Param predates the creation of these formats) such as Numpydoc, Google... I quite like Google's style which is less verbose than Numpy's one.

[MarcSkovMadsen]

I'm all in for the Google style. Use it every day.

[jbednar]

Right; Param predates just about everything good in Python, and its docstrings are a historical record of whatever trends may have prevailed at a given time over the past couple of decades. I'm happy with Google style.