Include academic references in module and class documentation when appropriate

[sbenthall]

NumPy's doc standards are for scientific libraries and there are conventions for how to include academic references in the docstrings. See point (14) here:

https://numpy.org/doc/stable/docs/howto_document.html#sections

Whether the references be academic articles (i.e. Krussel and Smith) or lecture notes, our docs would look better if we used this standard.

[sbenthall]

Test if this works with Sphinx and if so, use it