add stringify helper

via @jsoverson on IRC

It works, which is good. EventEmitter2 has what looks like some issues unregistering listeners, and communication involving cyclic structures breaks when jsonifying data. I had to implement a custom stringify method that might be beneficial to incorporate into the lib.

The issue names no files, tests, or entry points; begin by locating the library's JSON communication and listener-management code. Done means incorporating a stringify helper so communication involving cyclic structures no longer breaks, with the EventEmitter2 concern clarified or scoped.

Written by the indexing model from the issue text.