Add DatasetReader based on PyTorch

combo/data/__init__.py

combo/data/dataset_readers/__init__.py

...dataset_readers/classification_textfile_dataset_reader.py

combo/data/dataset_readers/dataset_reader.py

combo/data/fields/label_field.py

combo/data/token_indexers/__init__.py

...dexers/pretrained_transformer_fixed_mismatched_indexer.py

combo/data/token_indexers/pretrained_transformer_indexer.py

...ken_indexers/pretrained_transformer_mismatched_indexer.py

combo/data/token_indexers/single_id_token_indexer.py

combo/data/token_indexers/token_characters_indexer.py

combo/data/token_indexers/token_features_indexer.py

combo/data/token_indexers/token_indexer.py

combo/models/encoder.py

test.tsv