Implement local echo (a la mosh) about eternalterminal

[MisterTea]

I could do some naive thing such as drawing a letter when someone inputs it, then backing up when the next byte comes in. The issue is that I don't know how portable this is. Because mosh is itself a terminal emulator, it knows exactly what/where it drew in a predictive way so it can revert it correctly every time. If we had deep integration with a terminal emulator such as hyper.js or iTerm, then they could do the input prediction at their layer with more accuracy.

Either way, I'll try it and let's see what breaks.

[MisterTea]

I tried to implement this but it's a total nightmare without having control of the terminal emulator. This would be a good feature to add to hyper.js or some terminal emulator, but it doesn't belong at this layer.