* - Added pattren matcher for LSTM cell

* WIP added support to replace lstm cell instead of subgraph

* WIP LSTM pattern matcher, fuses recurrent cells

* WIP added RNN CPU op

* WIP mkldnn emmiter code for fprop RNN

* WIP RNN mkldnn integration
- Added mkldnn kernel for uni directional LSTM in the CPU emitter

* add a getter for root node

* recurrent graph rewrite

* fix perms, rename match_root -> get_match_root

* fix comp errors

* make match_root return the topmost match; fix tests

* - WIP GetOutputElement for handling multiple LSTM o/ps
- use RecurrentGraphRewrite for replacing node after matching LSTM cells

* WIP LSTM multi Output + debug prints

* moved LSTM fusion to cpu_fusion

* WIP added RNN superfused OP

* WIP towards RNN layer fusion

* WIP multiple output slicing RNN

* WIP RNN mulitple o/ps fusion across layer

* WIP corrected input params for fused RNN OP

* concat corrosponding param's across differnt LSTM to form inputs to RNN fused op

* i) Added  test case for RNN kernel ii) runs without error's

* refactored and moved LSTM class to standalone file

* Rename RNN -> Rnn , LSTM -> Lstm

* WIP replace lstm slices to the consumer op

* Slicing works on multiple RNN layers

* fixed all bugs

* - Added CPU RNN Recurrent Fusion
- Added CPU LSTM fusion
- removed debug code
- style fix

* - Added support to compute src_iter and dst_iter instead of taking zero_memory_desc
- Added unit test to compute one LSTM cell

*  changed RNN op signature to accept number of states in basic unit of RNN(GRU/LSTM/ vanilla RNN) cell

* added sanity checks for RNN op

* Fixed issue related to patching the graph while replacing the RNN sliced outputs

* Fixed issue to feed the input symbols in the order X0, X1, ...Xt to the RNN op

* Added unit test for multi layer RNN fusion

* Removed debug statements

* Added mulitlayered serialized graph ii) fixed compilation issue

* Addressed PR comments

* i) WIP MKLDNN layout for RNN Op ii) added test case for INTERPRETER v/s CPU Rnn results

* - Fixed bug w.r.to src_layer feature size in rnn mkldnn emitter code
- Refactored cpu_fusion rnn test case

* merge origin/master with branch pruthvi/lstm_fusion

* style fix

* Added test case for multiple RNN layers

* i) make rnn as mkldnn op if it meets the constraints ii) assert if rnn is not mkldnn op

* fix unit test failure

* - Added support to reliabily identify the hiddent state and input symbols from the nodes collected by Pattern matcher
- Fixed failing unit tests

* style fix

* - removed "node type" dependency to replace the intermediate LSTM outputs

* Addressed PR comments

* Fix unit test

* - added MKLDNN emitter for LSTM op
- graph pass to concat LSTM input recurrent state tensors
- CPU layout assignment for LSTM Op
- Fixed bug in rnn/lstm unit test's
- made changes to use replace_output instead of replace_node for replacing matched graph nodes in LSTM/RNN fusion pass

(cherry picked from commit d16fc709265cc0a73e60c6d5f6d2878e7b908aca)

* style fix

* Renamed passes and style fixes