Add typing and other tweaks

[tekktrik]

1. Adds type annotations like other libraries are getting
2. Changes a few instances of checking whether value is True OR False to isinstance() which is more Pythonic. Happy to revert if this was done for a specific reason
3. Updates Sphinx formatting in docstrings so things are clearer, or will display properly based on the hardships I've had with Sphinx haha. Can't confirm they help (or that anything was actually wrong yet) since documentation isn't viewable yet.

[tekktrik]

Here is the equivalent PR for the FRAM library: https://github.com/adafruit/Adafruit_CircuitPython_FRAM/pull/33