* init trieconcat_op

* add basic implementation

* add test

* add more test

* update unit test

* add PackAllSteps test

* fix PackAllSteps

* all test passed

* clean code

* remove state inside helper

* rename prob to score

* optimize RemoveFromEnd

* use deconstructor to delete BeamNode recursively

* optimize interface

* add comment to interface

* optimizer data structure

* use template to define the type of score

* use template parameter for BeamHelper

* change father to parent

* rename TrieConcat to BeamSearchOutConcat

* use LoDTensorArray

* rename BeamSearchOutConcat to BeamSearchDecode

* refine code

* remain all candidate sentence in beam_search_decode_op, do not consider endid

* use unique_ptr

* fix compare bug

* fix lod compile problem

* fix seq_concat with refactaring LoD

* fix failed unit test

* rename function name

* Adding documentation for seq_expand

* Adding documentation for seq_concat_op

* Adding documentation for sequence_conv

* Adding sequence_pool

* Fixing review comment

* Adding sequence_softmax

* Updating doc for sigmoid_cross_entropy_with_logits

* Polish the documentation for uniform_random and top_k ops

* Polishing more operators

They are public now