get shoppers|8

Args:
    train_df(dataframe): Pandas dataframe
    text_column(str): name of column containing the text
    label_columns(list): list of columns that are to be treated as labels
    val_df(dataframe): file path to test dataframe.  If not supplied,
                           10% of documents in training df will be
                           used for testing/validation.
    max_features(int): max num of words to consider in vocabulary.
                       Note: This is only used for prepro