Picodrive 1.14, less experimental Sega/Mega CD support

Update, finally. Here comes the changelog:
PCM sound implemented. Sonic soundtrack is complete now.
Savestates fixed
Improved compatibility: many games now boot, but most of them are glitchy.
Bugfixes, optimizations.
As promised, Snatcher boots now (at least my US version does). Not sure how long you can progress until it hangs As a bonus, Lunar boots too. A bit glitchy, but works. Oh and many other games run too. But most of them have severe graphic glitches and you won't see a thing

PCM slows things quite a bit if a lot of channels are used. This is not because it's emulation needs lots of calculations, but because of amount of data, which needs to be moved around (it can do 8 channels @ 32kHz). Switching audio to 22kHz improves things a bit.

detailed changelog:
Region autodetection now can be customized.
When CDDA music tracks changed, old buffer contents were incorrectly played. Fixed.
BRAM is now automatically formatted (no need to enter BIOS menu and format any more).
Games now can be reset, CDDA music no longer breaks after loading another ISO.
Fixed a race condition between 920 and 940 which sometimes caused CDDA music not to play.
Savestates implemented for Sega/Mega CD.
PCM sound added.
Some mixer code rewritten in asm. 22kHz and 11kHz sound rates are now supported in Mega CD mode (but mp3s must still always be 44kHz stereo).
Timer emulation added.
CDC DMA tansfers fixed. Snatcher and probably some more games now boot.
2M word RAM -> VDP transfers fixed, no more corruption in Ecco and some other games.