Add possibility to listen to a handle

[emilebres]

Hi, node-q is looking great!

However I noticed that it was not possible to listen on a handle as you can in q:

• h[]; if h is your handle

I needed this feature for my application so I added it and I thought I would make a pull request.

Let me know if there is any problem. Cheers

[michaelwittig]

cool stuff :)

[michaelwittig]

released as node-q@2.2.0