NUCLEO-F103RB: fixed erroneous MCU setting in Makefile
Introduced the CORTEX_ENABLE_WFI_IDLE flag in all chconf.h files, so the MCUs will enter sleep mode whenever the system is idle.
Enhanced and fixed several module specific files.
Changed all header guards so they will not use unserscores as pre- and postfix.
Introduced support the STM32F103 NUCLEO module.