Redocumented all device demos, now that they have changed over to the new USB class drivers.
Added C linkage to class drivers for C++ support.
Added prefixes to most of the class driver constants to prevent name clashes.
Removed scheduler and memory allocation libraries.
Added new EVENT_USB_StartOfFrame event in the library to indicate the start of each USB frame (when generated).
Removed Tx interrupt from the USBtoSerial demo; now sends characters via polling to ensure more time for the Rx interrupt.