Mark3 RTOS Source

-Resetting default config to use tickless timers
-Fixing timing prescaler on 2560

Adding support for atmega2560

Reverting de-optimization in cm4f build.
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-Fixing kernel bug. Corner-case where multiple threads are initialized at the same highest priority level before the kernel is started. The first thread that runs won't relinquish control until it voluntarily blocks. The fix ensures that round-robin scheduling is properly applied in this case.
-Adding set_target.sh script, allowing for developers to quickly reconfigure the build environment and switch from one target to another quickly.

Cleaning up tabs. Making sure that cortex m3/m4 files are not misrepresented as cortex m0 in the headers. Documentation for those ports needs more work, however.

- Adding preliminary cortex m4-f support
- Fixing usage of isb in cortex ports for control register modification
- Fixing demo stack-size usage in thread init.

- Cleaning up cortex m0 + m3 ports.
- Optimize context switching for m3 and up, which has a more capable ldmia/stmia.

-Ensure that the official test suite is only built for AVR, and not for other architectures where support for kernel-aware debugging, and built-in drivers may not exist.

Improvements to preliminary cortex m3/4/7 port.

- Removed superfluous code that was brought in out of desparation yesterday
- Cleaning up stuff, now that I know the fundamental code works
- Fixing linker args correctly so that "undefined reference to 'x'" doesn't occur

Adding rough kernel setup example for cortex m3