Brief Description of Fix

Right now, our documentation lists inputs and return values, but it does not include information about what types of errors functions normally raise. This is helpful information if you're working with try/except blocks, so that you know what errors to expect. And just as a matter of completeness, it's good to know all the outputs of a function, including likely errors.

Relevant Context

This would pretty much apply to every docstring, though I'm guessing we'll just add them piecemeal. According to my very poor understanding of Sphinx (I'm looking at here), we should be able to add documentation like

:raises: ValueError, TypeError

as we go along.