Fix HID class device driver -- if a SetIDle request is issued with the LSB of wValue set to zero, the idle period must be set for all HID interfaces.

Fix Keyboard and Mouse demos, Idle period is now multiplied by 4 as the period is read into and sent out of the device to ensure it is always stored as a multiple of 1ms. Fixes Keyboard demo using an initial Idle period of 2s rather than 500ms (thanks to Brian Dickman).

Move out the internal device serial descriptor reading routine into a seperate static function, rather than being part of USB_Device_GetDescriptor.

Added parameter directions to function parameter documentation.

Added new experimental FAST_STREAM_FUNCTIONS compile time option to speed up stream transfers at the expense of a higher FLASH consumption (needs testing to verify improved throughput).

MIDI device demo no longer blocks if a note change event is sent while the endpoint is not ready.

Move new Class Driver powered demos to a new ClassDriver subdirectory, re-add old low level demos to a LowLevel subdirectory.