Allow faking a tty for tests that need it

[bengl]

Either for all modules as a global option, or one a module-by-module basis as part of their config in lookup.json.

Using something like https://github.com/chjj/pty.js

This is to help stop issues like nodejs/node#8138 before they're released.

[MylesBorins]

I believe @bcoe was looking into this. Did you have nay progress?

[addaleax]

@thealphanerd as far as yargs is concerned, yargs/yargs#597 should take care of it. Having pty support in citgm might be still nice to have, though.

[Fishrock123]

Having some sort of instruction to use pty.js instead of the regular stdio options when spawning a new process is probably all that is needed here?

Unfortunately I think most people don't even know about that sort of difference.