 pretrained word vectors
                  - 'bert' for BERT Text Classification
                  - 'distilbert' for Hugging Face DistilBert model

    train_data (tuple): a tuple of numpy.ndarrays: (x_train, y_train) or ktrain.Dataset instance
                        returned from one of the texts_from_* functions
    preproc: a ktrain.text.TextPreprocessor instance.
             As of v0.8.0, this is required.
    multilabel (bool):  If True, multilabel model will be returned.
                        If 