Add docstrings

[adamltyson]

And host API docs on the website

[K-Meech]

Currently there's a mix of docstring styles used in this repository e.g. numpy style vs sphinx style. Is there a default docstring style used for brainglobe? @alessandrofelder @willGraham01

[adamltyson]

It should be numpy (although obviously we haven't followed that convention yet).

If the BrainGlobe docs don't specify any particular standard (although they should!), we fall back to the Neuroinformatics Unit standards.

[K-Meech]

Thanks for the clarification @adamltyson ! As far as I can see, there isn't a docstring standard listed in the BrainGlobe docs - I'll go ahead and open an issue to fix that