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.
- Make second 8355 into ROM expansion slot that can load custom 8755 programs
- Add software list for expansion ROMs, including Peter Naszvadi's version of Mastermind
- Add optional TTY interface
- Improve accuracy of button labels and change key bindings
- Add vectored interrupt and soft reset buttons
