Adds additional docstrings for `adafruit_gps.GPS` attributes. Thanks awordforthat for adding and jkittner for bug catching!
To use in CircuitPython, simply install the [Adafruit CircuitPython Bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-gps`.
Read the [docs](http://circuitpython.readthedocs.io/projects/gps/en/latest/) for info on how to use it.