Add block of memory to the end of the message, as a new frame.
Returns 0 on success, -1 on error.

def addmem(self, data, size):
        """
        Add block of memory to the end of the message, as a new frame.
Returns 0 on success, -1 on error.
        """
        return lib.zmsg_addmem(self._as_parameter_, data, size)