Sequence Scatter Op

* Add python api for expand op.

* Fix unitest.

* Remove 'out' from arguments and fix code style.

* fix API.spec

* Fix API

* Fix unitest

* loosen the restriction of output_size in conv2d_transpose

* test and docs

* fix code style

* fix ci test error

* bug fix

* fix python3 issue

* hide program APIs

* fix merge error

* update

* refine seq_softmax_op

* fix seq_softmax

* use cub in seq_softmax

* Add sequence_expand_as_op

* follow comment

* Enhence generate_proposal_labels_op
* Fix bug in generate_proposals_op
* Refine rpn_target_assign_op.
* by Bu Xingyuan, Wang Guanzhong and Dang Qingqing

* add ignore index

* update api.spec

* enhance softmax_with_cross_entropy

* Add intermediate

* fix flatten/squeeze/unsqueeze

* Considering compatibility issues, we could not fix the origin op

* follow comment

* reset the shape of XShape

* reimplement auc in pyton

* reimplement auc in fluid

* add auc unittest


* replace new auc in layers


* add batch Auc in Fluid

* name formated

* Fix bug in generate_proposals_op.
* Fix data type for RoIs.
* Refine and fix rpn_target_assign_op.
* Add the missing file bbox_util.h
* Rename BoxEncoder to BoxToDelta

* Add pad2d op.

* Add unitest and python api.

* Fix cuda op kernel.

* Fix python api.

* Fix python api.

* Update API.spec.

* Fix python api

* Add unit test for rpn_target_assign API.

* Add generate_proposal_labels for Faster-RCNN.

* Add proposals generation operator for Faster-RCNN.

* Polish PrintOp

* Polish PrintOp

* Polish PrintOp

* Refine test_print_op

* enhance pad_constant_like_op

* add API

* add API

* refine dist train RPC deps

* clean up

* clean up

* fix ut

* remove input for fetch_barrier

* follow comments

* fix auc layer and add check for auc op

* use input to check if states are inited

* optimize code