Docs are here: http://tannewt-micropython.readthedocs.io/en/microcontroller/
It differs from upstream's machine in the following ways:
* Python API is identical across ports due to code structure. (Lives in shared-bindings)
* Focuses on abstracting common functionality (AnalogIn) and not representing structure (ADC).
* Documentation lives with code making it easy to ensure they match.
* Pin is split into references (board.D13 and microcontroller.pin.PA17) and functionality (DigitalInOut).
* All nativeio classes claim underlying hardware resources when inited on construction, support Context Managers (aka with statements) and have deinit methods which release the claimed hardware.
* All constructors take pin references rather than peripheral ids. Its up to the implementation to find hardware or throw and exception.
This commit also introduces a new shared-bindings directory which is used to store the common Python -> C binding code. By having a shared directory we can ensure that the Python API across ports is the same. Each port will have a corresponding common-hal directory which provides definitions for the C api used in the shared-bindings code. That way the compiler can enforce the C api.
To migrate to this new shared API create a common-hal directory within your port and change the Makefile to compile both the shared-bindings and common-hal files. See atmel-samd/Makefile SRC_BINDINGS for an example.
