Vel factory function

def create(input_block: ModelFactory, rnn_type: str, hidden_layers: typing.List[int],
           output_dim: int, dropout=0.0):
    """ Vel factory function """
    def instantiate(**_):
        return MultilayerRnnSequenceModel(
            input_block.instantiate(), rnn_type=rnn_type, hidden_layers=hidden_layers, output_dim=output_dim, dropout=dropout
        )

    return ModelFactory.generic(instantiate)