* Added support for fused ReLU and dropout into transducer joint

* Reorganized code selection path in transducer joint fwd
* Added support for fused ReLU+dropout into transducer joint

* Vectorize transducer loss backward with fused softmax (#3)

* Nanz/transducer loss (#4)

* Vectorize transducer loss backward with fused softmax

* Added a predicate to avoid potential IMA

* Nanz/transducer loss (#5)

* Vectorize transducer loss backward with fused softmax

* Added a predicate to avoid potentional IMA

* Added more predicates to avoid IMAs

* Updated documentations for newly added features.

* Fixed a error in transducer.py