Type hints for documented API #77
Description
We should add type hints for the functions in our documented API.
Considerations:
- priority is not terribly high; type hints are typically not useful in a notebook environment, and that's probably often where this library is being used
- a lot of our returns are json or dataframes, where the raw return type is not very informative; we'd have to decide if we wanted to improve on that, and if so, how (ie, specifying json schemas or dataframe columns or something)