Full Due support, maskIRQ function

- Tested and now fully functional on Arduino Due
- Added support for the extended SPI functions: brings Due performance
up to par with Due managing the CSN   pin and settings
- Corrected issues with printDetails() on Due
- Changed added variables to staticly defined types: ie: uint16_t
instead of unsigned int
- I think this will work on all ARM based boards that use the Arduino
libs
- Added maskIRQ function - to be used in RF24Network sleep mode
- Changed csn(int mode) to csn(bool mode)
- Updated GettingStarted_CallResponse.ino example: Capture start time
AFTER printing to serial so measurement is more accurate