Set the Content-MD5 response header. Calculated from the the
        response body by creating the MD5 hash from it.

def set_response_content_md5(self):
        """Set the Content-MD5 response header. Calculated from the the
        response body by creating the MD5 hash from it.
        """
        self.response.content_md5 = hashlib.md5(self.response.body).hexdigest()