Enhanced class drivers to use the same public/private section seperations as other portions of the library.

Split out common defines/types from class drivers into a seperate common class driver directory.

Make central USB Class driver dispatch headers, used for both device and host modes.

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

Moved out each demos' functionality library files (e.g. Ring Buffer library) to /Lib directories for a better directory structure.

Renamed Serial_Stream driver to SerialStream to remain consistent with the rest of the library's naming scheme for files.

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.