Eternal Terminal control mode

Hey devs,

I'm a big fan of iTerm + tmux control mode ( https://gitlab.com/gnachman/iterm2/wikis/TmuxIntegration ). Unfortunately this only works on iTerm, which is only on OS/X. Several people have asked for some spec/doc so we could port this to another terminal emulator but there doesn't seem to be any standard ( see https://github.com/tmux/tmux/issues/763 and https://groups.google.com/forum/#!topic/tmux-users/e3Nrs0VJsDE ).

I'm also the lead dev on Eternal Terminal which is an alternative to mosh/ssh ( https://mistertea.github.io/EternalTCP/ ). I am thinking about making a control mode in ET that would replace tmux control mode. Here's how it could work:

1. Someone calls et -c hyper myhost:myport
2. ET sets up a bidirectional pipe between itself and Hyper and launches Hyper
3. Hyper writes commands to stdout (such as to make a new window, resize a window, input text on a certain terminal, etc.).
4. Hyper reads ET commands from stdin (such as output for a specific terminal, notification when a terminal has closed, etc.)

I would like to know your opinions on this before I commit time to it. Let me know, thanks!

No files, tests, or entry points are named in the issue. Clarify the control-mode protocol and implementation scope before starting; done would be an agreed design for ET and Hyper integration.