Fixed ATTACK_TIME value, added PORTAMENTO and CHORUS values. Thanks deckerego and rimwolf-redux!
To use in CircuitPython, simply install the [Adafruit CircuitPython Bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-midi`.
Read the [docs](http://circuitpython.readthedocs.io/projects/midi/en/latest/) for info on how to use it.