Add documentation (docstrings) to all methods

[jonespm]

All methods should include documentation about what they do. Most of this code doesn't have that.

We've been using the Sphinx format for other projects
https://sphinx-rtd-tutorial.readthedocs.io/en/latest/docstrings.html

This will fix some Codacy issues related to docstrings and also make the code easier to maintain in the future.