node cluster to speed up launching of commands

[jdx]

somewhat inspired by https://github.com/josephfrazier/prettier_d

one way we could dramatically speed up commands would be to use node cluster (or some kind of local daemon) to keep a group of command runners loaded and ready then when you run heroku foo it would send one of these preloaded runners to dispatch the command.

This is tricky because you no longer have access to the tty at this point. You would probably have to communicate to the running command that it is running as tty and assume it is from that point. I've looked into this in the past and this was a dealbreaker before, but with v6, it might be possible since we already wrap all of the output.

It's very much hopes-and-dreams state right now, but one day it could be a way to make commands run almost instantaneously.

If we wanted to do this, first it would be good to come up with a demo version of it.