Add support for synchronized output to prevent tearing

[JakeWharton]

If I run an application which continuously sends large chunks of text + ANSI control sequences to stdout, I sometimes see the cursor jump to the middle of the rendering. The application is enabling mode 2026 and sending the end-of-frame sequences. VHS should track whether this mode is enabled and not re-render a frame until it sees the end-of-frame sequence.

More details available at https://gist.github.com/christianparpart/d8a62cc1ab659194337d73e399004036

[Delta456]

Is this Windows? I can't reproduce this on Linux and Mac.

[JakeWharton]

I'm on Mac. I can try to write a repo. I suspect two echos each having half the sync marker with a sleep in between might do it.

[Delta456]

Please do