Add support for CloudSearch 2013 via cloudsearch2 module

This change is an extension of @aronrosenberg's #2211, which implements the 2013 API version. This pull request uses his code, but changes the following:

* Generated layer1.py from [service model](https://github.com/boto/botocore/blob/develop/services/cloudsearch.json)
* Layer1 -> CloudSearchConnection 
* Layer1 now uses JSON instead of XML responses
* Updated layer2 objects to use JSON and generated layer1
* Updated doc service to remove attributes which are no longer valid
* Updated search service to remove attributes which are no longer valid and
  modify existing attributes which have changed
* Updated unit tests and integration tests for all of the above

@aronrosenberg, @jamesls please review. An updated tutorial is in the works and will be added in a later commit.