Moved all examples to DuinoCube library

This way they can be accessed through the Arduino IDE.
DuinoCube: Rename library files to be shorter
DuinoCube: Rename defs.h to core_defs.h
DuinoCube: Add updated Core API declarations
DuinoCube: Replace "DuinoCube" prefix with namespace

e.g. class DuinoCubeCore becomes class Core within namespace DuinoCube.
DuinoCube: Add new Core API functions: system control

Updated core_usb_demo to test out the new API.
DuinoCube: Add Core functions to load data from files

Load directly from files.