Added Google Maps v3 API

Added the maps v3 api as a separate option so as not to break users of
the v2 api. Added support for v3 premier customers. Added support for
reverse geocoding. Added ability to access xml or json object after
running a geocode.
Removed output_format and xml from googlev3.

output_format is deprecated anyway, and json is easier to work with.
Also removed format_string. Similar results can be achieved using
geocode's bounds and/or region options.
Comment
Merge pull request #2 from jbouvier/master

Google v3 support + premier support