Creates a new webhook for the specified events (an array of strings). 
        Valid events are "Subscribe", "Deactivate", and "Update".
        Valid payload formats are "json", and "xml".

def create_webhook(self, events, url, payload_format):
        """Creates a new webhook for the specified events (an array of strings). 
        Valid events are "Subscribe", "Deactivate", and "Update".
        Valid payload formats are "json", and "xml"."""
        body = {
            "Events": events,
            "Url": url,
            "PayloadFormat": payload_format}
        response = self._post(self.uri_for("webhooks"), json.dumps(body))
        return json_to_py(response)