added support for Yahoo! BOSS Geo PlaceFinder
[placefinder] Remove httplib2 dependency

* Remove dependency on httplib2
* Raise ImportError on missing oauth2 late to
    avoid dependency for users of geocoding
    services other than Yahoo BOSS
Merge pull request #1 from philipkimmey/master

[placefinder] Remove httplib2 dependency
made small changes for code consistency, removed Geocoder error for no results
fixed error handling to use urllib HttpError instead of the httplib style
Merge pull request #20 from jhmaddox/master

Yahoo! BOSS Geo PlaceFinder support