Cleanup and adding more needed files

cores/arduino/USART.cpp

cores/arduino/USART.h

cores/arduino/build_gcc/libarduino_adk2.mk

cores/arduino/build_gcc/libarduino_arduino_due_u.mk

cores/arduino/build_gcc/libarduino_arduino_due_x.mk

cores/arduino/build_gcc/libarduino_sam3s_ek.mk

cores/arduino/build_gcc/libarduino_sam3u_ek.mk

cores/arduino/build_gcc/libarduino_sam3x_ek.mk

cores/arduino/validation/build_iar/test.ewd

cores/arduino/validation/build_iar/test.ewp

libraries/SPI/SPI.cpp

libraries/SPI/SPI.h

...les/BarometricPressureSensor/BarometricPressureSensor.ino

...ries/SPI/examples/DigitalPotControl/DigitalPotControl.ino

libraries/SPI/keywords.txt

libraries/Wire/Wire.cpp

libraries/Wire/Wire.h

...aries/Wire/examples/SFRRanger_reader/SFRRanger_reader.pde

.../examples/digital_potentiometer/digital_potentiometer.pde

libraries/Wire/examples/master_reader/master_reader.pde