Added a Protocol for hardware objects with read-only and read/write `value` properties (e.g., `analogio.AnalogIn`, `digitalio.DigitalInOut`, etc).
To use in CPython, `pip3 install adafruit-circuitpython-typing`.
Read the [docs](http://circuitpython.readthedocs.io/projects/circuitpython-typing/en/latest/) for info on how to use it.