Add API method places#search [bounty #18]

The places#search action is reachable through the ```/search/:radius/:lat/:lng``` route and returns a list of places in the given range ordered by distance.

The only format this action accepts is JSON, and this is an example of it's use:

http://localhost:3000/api/v1/places/search/1000/-23.0058447/-43.3214268.json