Feature/node ipc channel

IPC channel for parents to make requests of their children... and vice versa.

Preparation for strong-pm to communicate with strong-supervisor using node IPC.


I can't return the currently attached instance, it has the wrong onRequest. And I think throwing is better than stealing the last one, and replacing it's onRequest with the new one... And you'll note there is no close API anywhere here... :-) (YGNI, yet, anyhow).

I'd like to leave the cluster API alone in this PR, which didn't introduce any changes to it [1]. This code we are discussing was just rearranged to allow sharing with process.js, the new code here is all in d761b455f33e.

[1] OK. I confess I added createServer being exported on line 128, it just seemed symetrical with all the other components, but I can delete that line.