Haravan

* Made HaravanResource.clear_session idempotent.

* Use the correct redirect parameter in Session.create_permission_url.
Was redirect_url but corrected to redirect_uri.

* Added support for OAuth2.
* HaravanResource.activate_session must now be used with OAuth2 instead
of setting HaravanResource.site directly.
* Session.__init__ no longer allows params to be passed in as **params
* Session.__init__ now makes an HTTP request when using OAuth2 if
params are specified
* Session now exposes the access token through the token instance
variable to simplify session saving and resuming

* Using setup.py no longer requires all dependancies
* More compatiblity fixes for using the latest pyactiveresource
* HaravanResource.activate_session is not recommended over setting site
directly for forward compatibility with coming OAuth2 changes.

* Compatiblity fixes for using latest (unreleased) pyactiveresource

* Added support for customer search and customer group search.
* Resource erros are cleared on save from previous save attempt.
* Made the library thread-safe using thread-local connections.