Adafruit-circuitpython-mpr121

- Added `setup.py`
- Added PyPI release info to `.travis.yml`
- Updated `requirements.txt`
- Added a more comprehensive `.gitignore`

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

To use in CPython, `pip install adafruit-circuitpython-mpr121`.

Read the [docs](http://circuitpython.readthedocs.io/projects/mpr121/en/latest/) for info on how to use it.

Thanks to sommersoft for the documentation refinement.

To use in CircuitPython, download the .mpy file and copy it to the `lib` folder on the `CIRCUITPY` drive. Or, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

Read the [docs](http://circuitpython.readthedocs.io/projects/mpr121/en/latest/) for info on how to use it.

Updated to fix issue with `pip install` info.

Library updated with lint.

Thanks to tannewt for the great work!

Changes made to follow changes in Adafruit_Circuitpyton_BusDevice.I2CDevice

Fix for new I2CDevice API. Make sure your [CircuitPython](https://github.com/adafruit/circuitpython) and libraries are up to date!