Get rid of a couple of copies of the CC0 text. Add header comment to
CC0 files to remind people editing them what the terms are. Also add
some missing XML headers. The header comments in layouts won't bloat
the binary - they get stripped out before compressing, same as any other
comments.
This also means that it now uses the software list system instead of
loading the floppy disk image into a memory region. To run the driver
use: "mame guab -flop guab3" now. You may also just start the driver,
then choose a floppy disk image from the builtin file manager.
