add a patch method

[JensTimmerman]

 +    def patch(self, url, body=None, headers={}, **params):
 +        """
 +        Do a http patch request on the given url with given body, headers and parameters
 +        Parameters is a dictionary that will will be urlencoded
 +        """
 +        url += self.urlencode(params)
 +        return self.request(self.PATCH, url, json.dumps(body), headers)

[jpaugh]

Thanks a bunch! This closes up one of holes in our Github API support.