Snes9x EX+

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* Update core to latest GIT
* Add a rewind button to the stock top-left virtual controls and only the show the rewind button when rewind states are set in the system options
* Add Options -> Frame Timing -> Low Latency Mode to keep the emulation thread in sync with the renderer thread to prevent extra latency, turned on by default but trying turning off in case of performance issues
* Default to the screen's reported refresh rate as the output rate if the device supports multiple rates