v2.0
* Various components have been rewritten to simplify the API and make it easier
  to extend without breaking backwards compatibility. This release /does/ break 
  backwards compatibility:
** Indicators() is now IndicatorAPI(), Climate() now ClimateAPI().
** For both APIs, the main data methods return custom models, rather than
   namedtuples. 
** get_country_indicators() becomes get_dataset(), and returns one dataset
   rather than multiple indicators.
** Climate API is replaced with two methods, get_instrumental() and
   get_modelled().
** Various API variables have been rearranged, eg. climate API code definitions.
* Supports python 2.6+ and python 3. 
* Full tox test suite.
* Can access the raw JSON API responses.
* Fix handling of all non-ISO region codes (eg. A1) for the indicator API. 
* The climate API has various simplifications, eg. removing GCM
  and ensemble parameters. The as_dict() method takes a "sres" arg, so the
  returned data only has one datum per year. 
* Can return dictionary date keys as datetime objects rather than strings.
* Moving forwards, dataset models can be extended to return new formats (eg.
  pandas), without further breaking compatibility.
