Tools: AVRPDF: Create XMLDeviceParser base class.
AVRPartDescriptionFile now inherits from this class,
which allows a cleaner abstraction and future addition
of parsers for other devices.
Tools: AVRPDF: Rename AVRDevice to Device, since it is very generic.
Clean up the names of some local variables.
Tools: Move avr_part_description_files to device_file_generator