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.
variants better
sitcom: implement Boot and Reset buttons, implement remapping of low
32kB, hook up PIA, implement I/O space mirrors, hook up RS232 interface
for downloading programs, add a software list with two example programs.
(nw) sitcom software list isn't hooked up right, the file won't be fed
to the -bitb input if you run with the set name; you have to run like
mame sitcom -bitb roms/sitcom/san.zip/san.hex
