v2.0.0

• Ability to install through pip.
• Advanced layers are now organized into subfolders.
• New basic layers: Convolution over sequence, MaxMargin.
• New attention layers: Co-attention, multi-head attention, hierarchical attention.
• New encoders: Arbitrary sequence-of-vectors encoder, BiLSTMp speech feature encoder.
• New decoders: Multi-source decoder, switching decoder, vector decoder.
• New datasets: Kaldi dataset (.ark/.scp reader), Shelve dataset, Numpy sequence dataset.
• Added learning rate annealing: See lr_decay* options in config.py.
• Removed subword-nmt and METEOR files from repository. We now depend on
  the PIP package for subword-nmt. For METEOR, nmtpy-install-extra should
  be launched after installation.
• More multi-task and multi-input/output translate and training regimes.
• New early-stopping metrics: Character and word error rate (cer,wer) and ROUGE (rouge).
• Curriculum learning option for the BucketBatchSampler, i.e. length-ordered batches.
• New models:
  • ASR: Listen-attend-and-spell like automatic speech recognition
  • Multitask*: Experimental multi-tasking & scheduling between many inputs/outputs.