* USB CDC implement on SiM3u1xx
* USB stack base on LUFA
* MCU platform is SiM3U167 Arm Cortex M3 core.

Status
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* Change to USB ISR driven routine. 
* USB CDC class has been tested and works well.
* Support both 32 bit and 64 bit Windows
* Other classes need to be tested in future.

Aug 19, 2013
* Removed global interrupt mask macro which cause system interrupt work abnormal.