Adafruit-circuitpython-busdevice

- Added `requirements.txt` for Sphinx build
- Added `pylint` 1.9.2 force install to `.travis.yml`

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-busdevice`.

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

Update to install from pypi (using `pip`.)

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

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

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

from March updates.