Sockeye

Changed
- Updated to [MXNet 1.1.0](https://github.com/apache/incubator-mxnet/tree/1.1.0)

Added
- Source factors, as described in

Linguistic Input Features Improve Neural Machine Translation (Sennrich \& Haddow, WMT 2016)
[PDF](http://www.aclweb.org/anthology/W16-2209.pdf) [bibtex](http://www.aclweb.org/anthology/W16-2209.bib)

Additional source factors are enabled by passing `--source-factors file1 [file2 ...]` (`-sf`), where file1, etc. are
token-parallel to the source (`-s`).
An analogous parameter, `--validation-source-factors`, is used to pass factors for validation data.
The flag `--source-factors-num-embed D1 [D2 ...]` denotes the embedding dimensions and is required if source factor
files are given. Factor embeddings are concatenated to the source embeddings dimension (`--num-embed`).

At test time, the input sentence and its factors can be passed in via STDIN or command-line arguments.
- For STDIN, the input and factors should be in a token-based factored format, e.g.,
`word1|factor1|factor2|... w2|f1|f2|... ...1`.
- You can also use file arguments, which mirrors training: `--input` takes the path to a file containing the source,
and `--input-factors` a list of files containing token-parallel factors.
At test time, an exception is raised if the number of expected factors does not
match the factors passed along with the input.

- Removed bias parameters from multi-head attention layers of the transformer.

Changed
- Loading/Saving auxiliary parameters of the models. Before aux parameters were not saved or used for initialization.
Therefore the parameters of certain layers were ignored (e.g., BatchNorm) and randomly initialized. This change
enables to properly load, save and initialize the layers which use auxiliary parameters.

Changed
- Device locking: Only one process will be acquiring GPUs at a time.
This will lead to consecutive device ids whenever possible.

Changed
- Internal change: Standardized all data to be batch-major both at training and at inference time.

Changed
- When a device lock file exists and the process has no write permissions for the lock file we assume that the device
is locked. Previously this lead to an permission denied exception. Please note that in this scenario we an not detect
if the original Sockeye process did not shut down gracefully. This is not an issue when the sockeye process has write
permissions on existing lock files as in that case locking is based on file system locks, which cease to exist when a
process exits.