Added support for digital pins.

Currently class implementation is in gpioc2.h
Only the "pin output" functionality has been tested - input has not (but
is implemented).
Note: any program including the gpioc2.h header must be run as a superuser - read and
writes to the GPIO pins have restricted access.

README.md

@@ -1,2 +1,2 @@
 # Odroid-C2-GPIO
-Light-weight C++ class that allows access to GPIO pins on odroid.
+C++ class that allows access to GPIO pins on odroid.