Picodrive2x v1.20 - Sega Mega CD Emulation Improved

After some messing around with noiz2sa got back to my main project, mostly to implement missing stuff. Still no scaling/rotation chip support, but most other stuff is there now. Will do the gfx chip next, and then only the hard stuff will be left (timing problems and various bugs).

So this version has a good compatibility boost, which now should exceed 50% mark. Here are some games which can be made to work now (including some FMV ones, I mostly used this wishlist for testing):
Adventures of Willy Beamish
Final fight
Heart of the alien
Lunar 2 - eternal blue (textboxes fixed)
Night trap
Sewer shark
There is a new ultra-slow option called "better sync", which is similar to "Perfect synchro" in Gens. So all testers should try that if game doesn't boot. For example Popful mail and Vay needs it to boot, but after start that option can be disabled and they seem to run fine (at least their very beginning does). Report any hanging/glitchy games to me, so I can look at them.

Complete changelog:
Fixed a long-standing problem in audio mixing code which caused slight distortions at lower sample rates.
Changed the way 920 and 940 communicates (again), should be more reliable and give slight performance increase.
Some optimizations in audio mixing code.
Some menu changes (background added, smaller font in ROM browser, savestate loader now can select slots).
1M mode DMA transfers implemented (used by FMV games like Night Trap and Sewer Shark).
Games now can run code from WORD RAM in 1M mode (fixes Adventures of Willy Beamish).
"Cell arrange" address mapping is now emulated (Heart of the alien).
"Color numeric operation" is now emulated (text in Lunar 2, Silpheed intro graphics).
"Better sync" option added (prevents some games from hanging).
Savestates now go into their own directory (but may still be loaded from the working dir)