Headless Mode / Test Mode

[clydeshaffer]

• Don't load any windows, maybe don't even init SDL
• Optional command line arguments specify filenames for input relay file, output video, memory dump file after some duration.
• JSON/XML/TOML test description that specifies replay files along with post-test conditions to expect (color of certain pixels, frame flip count, audio activity)
• Possibly do test function outside of the emulator using the outputs instead of integrated? eg. Jest test that analyzes a video and memory dump. Might mean video has to be lossless format though.

[nickgirardo]

This would be very well appreciated!
Even just having some tests for the wdc 65c02 core would be tremendously helpful. I'm pretty sure there are some minor inaccuracies (aside from missing ops and known cycle inaccurate behavior) which continue to exist after my recent prs. Specifically the behavior of the flags when processing ADC/ SBC in decimal mode. Also, manually testing JMP (abs, x) was a total nightmare and I'm left only 98% sure it operates as intended :/