* corrected ld script for stack and heap initializations.
* enabled main() and infinite while loop after that in startup_samd21.c
* added UART_0 in PerpheralNames.h
* updated PeripheralPins.h, objects.h, device.h, PinNames.h for including UART
* added PeripheralPins.c
* Base Commit for Serial/UART in SAMR21 (added ASFcode from Atmel Studio and serial_api.c) - Not Working (To be updated with the new code)
* Removed rtc_count.h and rtc_count.c since we are porting rtc calendar driver from asf. Keep both drivers for the same peripheral make error in compilation after exporting.