PUT /config/(string: subject)

        Update the compatibility level for a subject.  Level must be one of:

        :param str level: ex: 'NONE','FULL','FORWARD', or 'BACKWARD'

def update_compatibility(self, level, subject=None):
        """
        PUT /config/(string: subject)

        Update the compatibility level for a subject.  Level must be one of:

        :param str level: ex: 'NONE','FULL','FORWARD', or 'BACKWARD'
        """
        if level not in VALID_LEVELS:
            raise ClientError("Invalid level specified: %s" % (str(level)))

        url = '/'.join([self.url, 'config'])
        if subject:
            url += '/' + subject

        body = {"compatibility": level}
        result, code = self._send_request(url, method='PUT', body=body)
        if code >= 200 and code <= 299:
            return result['compatibility']
        else:
            raise ClientError("Unable to update level: %s. Error code: %d" % (str(level)), code)