Vel factory function

def create(input_block: ModelFactory, rnn_type: str, output_dim: int,
           rnn_layers: typing.List[int], rnn_dropout: float=0.0, bidirectional: bool=False,
           linear_layers: typing.List[int]=None, linear_dropout: float=0.0):
    """ Vel factory function """
    if linear_layers is None:
        linear_layers = []

    def instantiate(**_):
        return MultilayerRnnSequenceClassification(
            input_block=input_block.instantiate(), rnn_type=rnn_type, output_dim=output_dim,
            rnn_layers=rnn_layers, rnn_dropout=rnn_dropout, bidirectional=bidirectional,
            linear_layers=linear_layers, linear_dropout=linear_dropout
        )

    return ModelFactory.generic(instantiate)