Update to MXNet 0.12.0

[1.10.1]

Changed

• Reduced memory footprint when creating data iterators: integer sequences
  are streamed from disk when being assigned to buckets.

[1.10.0]

Changed

• Updated MXNet dependency to 0.12 (w/ MKL support by default).
• Changed --smoothed-cross-entropy-alpha to --label-smoothing.
  Label smoothing should now require significantly less memory due to its addition to MXNet's SoftmaxOutput operator.
• --weight-normalization now applies not only to convolutional weight matrices, but to output layers of all decoders.
  It is also independent of weight tying.
• Transformers now use --embed-dropout. Before they were using --transformer-dropout-prepost for this.
• Transformers now scale their embedding vectors before adding fixed positional embeddings.
  This turns out to be crucial for effective learning.
• .param files now use 5 digit identifiers to reduce risk of overflowing with many checkpoints.

Added

• Added CUDA 9.0 requirements file.
• --loss-normalization-type. Added a new flag to control loss normalization. New default is to normalize
  by the number of valid, non-PAD tokens instead of the batch size.
• --weight-init-xavier-factor-type. Added new flag to control Xavier factor type when --weight-init=xavier.
• --embed-weight-init. Added new flag for initialization of embeddings matrices.

Removed

• --smoothed-cross-entropy-alpha argument. See above.
• --normalize-loss argument. See above.

[1.9.0]

Added

• Batch decoding. New options for the translate CLI: --batch-size and --chunk-size. Translator.translate()
  now accepts and returns lists of inputs and outputs.

[1.8.4]

Added

• Exposing the MXNet KVStore through the --kvstore argument, potentially enabling distributed training.

[1.8.3]

Added

• Optional smart rollback of parameters and optimizer states after updating the learning rate
  if not improved for x checkpoints. New flags: --learning-rate-decay-param-reset,
  --learning-rate-decay-optimizer-states-reset

[1.8.2]

Fixed

• The RNN variational dropout mask is now independent of the input
  (previously any zero initial state led to the first state being canceled).
• Correctly pass self.dropout_inputs float to mx.sym.Dropout in VariationalDropoutCell.

[1.8.1]

Changed

• Instead of truncating sentences exceeding the maximum input length they are now translated in chunks.