Merge branch 'pascal2' into 'master'

fairseq/fairseq/data/tags_language_pair_dataset.py

fairseq/fairseq/models/fairseq_model.py

fairseq/fairseq/models/faiseq_tags_encoder.py

fairseq/fairseq/models/pascal_transformer.py

...seq/fairseq/models/transformer/pascal/transformer_base.py

...q/fairseq/models/transformer/pascal/transformer_config.py

.../fairseq/models/transformer/pascal/transformer_encoder.py

fairseq/fairseq/models/transformer/pascal_transformer.py

fairseq/fairseq/modules/multihead_pascal.py

fairseq/fairseq/modules/transformer_layer.py

fairseq/fairseq/tasks/fairseq_task.py

fairseq/fairseq/tasks/tags_translation.py