Merge branch 'add-__hash__-to-models-opsgenie#38' into current

* add-__hash__-to-models-opsgenie#38:
  Define __hash__ for Responders model
  ...so it can be used in hashable collection.
  (This is a temporary patch to work around issue opsgenie#38)

opsgenie_sdk/models/responder.py

@@ -145,3 +145,6 @@ def __eq__(self, other):
     def __ne__(self, other):
         """Returns true if both objects are not equal"""
         return not self == other
+
+    def __hash__(self):
+        return hash(self.__dict__)