Thanks caternuson and ladyada.
Also thanks to dherrada for infrastructure changes (which don't change the library code).
To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-motorkit`.
Read the [docs](http://circuitpython.readthedocs.io/projects/motorkit/en/latest/) for info on how to use it.