* There are three kinds of cartridge: 32K flat, 16K fixed plus 16K
switchable, and 32K switchable. Cart implementation will come later.
-Various cleanups:
* gbcolor.xml: Proper Pinyin description for sqsd.
* sound/pokey.cpp: Minor cleanup, and got rid of an unnecessary member
in channel structures (only used in inline member functions).
* nintendo/gb.cpp: Spell Mega Duck with a space consistently.
* sega/turbo_a.cpp: Use an optional device finder to get discrete sound
device. The function that would add this seems to have been lost.
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.
