'Allows additional representation transformers to be declared for the
api. Transformers are functions that must be decorated with this
method, passing the mediatype the transformer represents. Three
arguments are passed to the transformer:
* The data to be represented in the response body
* The http status code
* A dictionary of headers
The transformer should convert the data appropriately for the mediatype
and return a Flask response object.
Ex::
@api.representation(\'application/xml\')
def xml(data, code, headers):
resp = make_response(convert_data_to_xml(data), code)
resp.headers.extend(headers)
return resp'

def representation(self, mediatype):

    def wrapper(func):
        self.representations[mediatype] = func
        return func
    return wrapper
