Add .on() function to zeromq and a test for it.
Merge branch 'zeromq-event' of https://github.com/panuhorsmalahti/DefinitelyTyped into panuhorsmalahti-zeromq-event
reference node/node.d.ts. not node/node-0.11.d.ts
Merge branch 'panuhorsmalahti-zeromq-event'