n text format.
If train and test contain additional subfolders that do not represent
classes, they can be ignored by explicitly listing the subfolders of
interest using the classes argument.
Args:
    datadir (str): path to folder
    classes (list): list of classes (subfolders to consider).
                    This is simply supplied as the categories argument
                    to sklearn's load_files function.
    max_features (int):  maximum number of unigrams to consider
                         Note: