v1.9.0

PRs accepted:
Cleaning up the code for gru/lstm as transition function for universal transformer. Thanks @MostafaDehghani !
Clipwrapper by @piotrmilos !
Corrected transformer spelling mistake - Thanks @jurasofish!
Fix to universal transformer update weights - Thanks @cbockman and @cyvius96 !
Common Voice problem fixes and refactoring - Thanks @tlatkowski !
Infer observation datatype and shape from the environment - Thanks @koz4k !

New Problems / Models:

• Added a simple discrete autoencoder video model. Thanks @lukaszkaiser !
• DistributedText2TextProblem, a base class for Text2TextProblem for large-datasets. Thanks @afrozenator!
• Stanford Natural Language Inference problem added StanfordNLI in stanford_nli.py. Thanks @urvashik !
• Text2TextRemotedir added for problems with a persistent remote directory. Thanks @rsepassi !
• Add a separate binary for vocabulary file generation for subclasses of Text2TextProblem. Thanks @afrozenator!
• Added support for non-deterministic ATARI modes and sticky keys. Thanks @mbz !
• Pretraining schedule added to MultiProblem and reweighting losses. Thanks @urvashik !
• SummarizeWikiPretrainSeqToSeq32k and Text2textElmo added.
• AutoencoderResidualVAE added, thanks @lukaszkaiser !
• Discriminator changes by @lukaszkaiser and @aidangomez
• Allow scheduled sampling in basic video model, simplify default video modality. Thanks @lukaszkaiser !

Code Cleanups:

• Use standard vocab naming and fixing translate data generation. Thanks @rsepassi !
• Replaced manual ops w/ dot_product_attention in masked_local_attention_1d. Thanks @dustinvtran !
• Eager tests! Thanks @dustinvtran !
• Separate out a video/ directory in models/. Thanks @lukaszkaiser !
• Speed up RL test - thanks @lukaszkaiser !

Bug Fixes:

• Don't daisy-chain variables in Universal Transformer. Thanks @lukaszkaiser !
• Corrections to mixing, dropout and sampling in autoencoders. Thanks @lukaszkaiser !
• WSJ parsing only to use 1000 examples for building vocab.
• Fixed scoring crash on empty targets. Thanks David Grangier!
• Bug fix in transformer_vae.py

Enhancements to MTF, Video Models and much more!