Mark3 RTOS Source

-Kernel port for CM0, however, is just a stub at this point, need to implement NVIC code for SysTick timer, as well as the gross inline-assembly for context switching.
-There's no board-specific init code tied into Mark3, so that would need to be linked in as well for any example code. Really, example code will have to be abstracted out by platform going forward
-Fixed some default usage of K_UCHAR arrays as the stack - Implemented new K_WORD type for platform-specific register word-width.