Thanks to ntoll for the fix!
To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://circuitpython.org/librares).
To use in CPython, `pip3 install adafruit-circuitpython-mpr121`.
Read the [docs](http://circuitpython.readthedocs.io/projects/mpr121/en/latest/) for info on how to use it.