Implemented general GPIO support across all types of pins.
Added support for aborting I2C transfers via callback.
Implemented driving PWM chip as an I/O expander (for driving MUX select lines).
Implemented reading and writing Legacy GPIO pins.
Updated some comments to Doxygen format.
Update wiring code for Dmap compatibility.
Removed code made obsolete by Dmap, or not yet implemented in Dmap, from arduino.h.
Modified wire.h to use new Dmap based I2C code.
Updated some comments.
Fixed hardware serial bug.
Use pin function lock functionality.