added an option to disable background "overlay"
changed background image when background is 'pure black'
improved some menu transitions
minor menu arrangement & code cleanup
* improved sprites processing accuracy.
* fixed VBLANK transition line checks.
* code cleanup and (minor) optimizations.
[Core/Sound]
* increased FM internal sample size to 32-bit to avoid overflow when adding channels.
* added preliminary emulation of YM2612 DAC precision (can be configured to match real console output).
* added configurable roll-off for FIR filtering in High-Quality FM mode.
[Wii]
*added support to enable/disable Video Encoder Trap Filter: can help reproducing "color blending" as on a real Genesis (composite video only).
*added support to configure Video Encoder gamma correction.
*fixed audio/video desync that could occur after loading a new game
*improved general synchronization of frame execution
*modified ASNDLIB shutdown to prevent potential memory leak with DSP tasks
*changed some global variables to use int type by default for optimization
*some code cleanup
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* improved 68k accuracy (initial reset timing + auto-vectored interrupts handling).
* modified Z80 & 68k cores to directly use external cycle count instead of intermediate counters.
* improved Z80 & 68k cpu execution/synchronization accuracy, now use Master Clock as common clock reference.
* improved PSG & FM chips synchronization with CPU execution (fixed point precision).
* completely rewrote sound output processing & mixing: sound chips are now clocked with exact output frame rate
to ensure 100% smooth video & audio playback, with no lag or skipping, while still rendering an accurate number
of samples per frame. This will also make fast-forward implementation (video AND sound) more trivial.
* improved color accuracy in VDP highlight mode to match results observed on real hardware.
* improved sprites processing timing accuracy: fixes (un)masked sprites in Mickey Mania (3D level), Sonic 2 (VS mode).
* improved horizontal blanking & HINT/VINT occurrence timing accuracy, as measured on real hardware.
* improved H-Counter accuracy in 40-cell mode, as measured on real hardware.
* optimized Z80 bus status signals
* usual code cleanup
[GCN/WII]
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fixed ASNDLIB exit when returning to game
fixed audio/video startup sync
modified audio back-end engine according to new audio processing core (see above)
