Notable (possibly breaking) changes:

• d45db80: Remove checkpoint utility functions from utils.py into checkpoint_utils.py
• f2563c2: Move LM definitions into separate files
• dffb167: Updates to model API:
  • FairseqModel -> FairseqEncoderDecoderModel
  • add FairseqDecoder.extract_features and FairseqDecoder.output_layer
  • encoder_out_dict -> encoder_out
  • rm unused remove_head functions
• 34726d5: Move distributed_init into DistributedFairseqModel
• cf17068: Simplify distributed launch by automatically launching multiprocessing on each node for all visible GPUs (allows launching just one job per node instead of one per GPU)
• d45db80: Change default LR scheduler from reduce_lr_on_plateau to fixed
• 96ac28d: Rename --sampling-temperature -> --temperature
• fc1a19a: Deprecate dummy batches
• a1c997b: Add memory mapped datasets
• 0add50c: Allow cycling over multiple datasets, where each one becomes an "epoch"

Plus many additional features and bugfixes