Port of BiLSTM-CNN-CRF for sequence labeling

[lintool]

Here's the repo from Reporting Score Distributions Makes a Difference: Performance Study of LSTM-networks for Sequence Tagging at EMNLP 2017.

The implementation is based on Keras 1.x and can be run with Theano (0.9.0) or Tensorflow (0.12.1) as backend.

We should port it to PyTorch.