Add annotations to all functions

[miloknowles]

Also low priority for now, but it would be nice to include types on all arguments and return types.

I propose that we wait until everything is refactored and in a more stable state, and then go through and add the types. I imagine you'll be doing a pass through the code to add more documentation/cleanup before the release anyways.

[grgmiller]

Guidelines on annotations: https://peps.python.org/pep-3107/