Searching

Heya,

Noticed that searching didn't seem to be supported yet so I added some code and tests to support Issuu's v2 search api  as outlined here in http://developers.issuu.com/api/search/

The response is a bit different from the normal v1 api document response, so I added a little conversion utility to have it respond with an array of Issuu::Document's but by default I figured just returning the json data they provide would be the best bet.

It also has the ability to do page searches though the default is document search.

Anyway thanks again for all your work, this gem definitely smoothed integration with Issuu.

-R