Add urban

Add an Urban Dictionary listener.
Using the JSON API it returns the first and best rated result with an example.
Line breaks in results are substituted with spaces.

result sample:
url: ```http://api.urbandictionary.com/v0/define?term=javascript%20programming```
We use comma-declarations elsewhere in the project: https://github.com/putaindecode/ed-209/blob/master/listeners/clly.js#L13-L15