Support non-native refresh rates and exact AV sync

[andrew-hoffman]

Should be able to provide a less jerky picture when the console is not running at the same refresh rate as the computer display, and blend frames instead of dropping them altogether.

Example Scenarios:

60 hz console on 50 fps display like most new Intel IGP laptops do on battery
50hz PAL console on 59.94 hz display
144 hz display (I don't know anyone with one of these yet)

-need to actually be able to detect frame rate of host PC! (and I can't even catch vblank with Swing)
-Nestopia automatically blends frames when they don't match. need fast frame blending (maybe CRT phosphor exponential decay emulation)
-APU sample rate will have to drift a bit so we get exactly lined up with vblank and no dropped frames or sound pops (can adjust output sample rate +/- 0.6% and no one should notice.)