Added missing documentation for AUDIO_SAMPLE_FREQUENCY configuration option in the audio device demos.

Fixed CDC demo not sending an empty packet after each transfer to prevent the host from buffering incomming data.

Altered Project and Bootloader makefiles so that the path to the LUFA library can be set in one place.

Seperated out OTG, Device and Host mode demos into seperate folders for clarity. Adjusted makefiles so that the path to the LUFA library can be set in one place.