GPU implementation for layer normalization operator.

* Refine load

* Address review comments: round 1

* Make API consistent with python-save/load

* Add another unit test

* Remove commented function

* Fix GPU bug

* Address review comments

* Modify wrt PR 8147

* Fix filenames for combined case

* Fix typo

* Address review comments: round 2

* Unify TestInference by keeping default param in template

* Address review comment

* Fix spacing

Add Inference example and unit test for rnn_encoder_decoder

* Fixing unbufered test to a generic test

* Update channel_test.cc

* splitting over functions

* add type

* fix *

* Adding more details to cluster_train

* Update copyright for notest_dist_image_classification

* Fixed copyright

* Updating the copyright year and content

Refine name of "RNN相关模型"

refine structure of cluster and quick start

Fix for program crash when destructor is called before channel close with blocked readers/writers (#8197)

* Fix destructor crash and add unit tests

* Fix typo in unit test

* Reword comments

* Make close channel a generic test

* Refactoring unit tests

* Fix method name

Fix/mixed vector

* Fix parallel.do with batch norm

* Change log level

* CopyShare AllPlaces

* disable nccl test

* bring back parallel_do test

add cpp_data_feeding.md

* init polynomial_decay

* test polynomial_decay

* complete polynomial_decay

* fix conditional block op

* init scalar-switch-case-op

* switch op can compile

* complete forward switch_op

* add GetMatchCaseIndex

* add switch_grad_op

* init switch Python API

* add test_switch

* support set block list in python

* fix scope problem

* complete test

* optimize test

* optimize test

* rm backward part

* clear grad op

* polynomial_decay use switch op

* revert conditional_block_op and reshape_op

* add piecewise_decay and test

* fix piecewise_decay

* try to use condition op for switch

* can work

* clean old code

* revert

* rm switch_op.cc

* optimize code

* add attr is_scalar_condition for condition_block_op

* fix comment

* fix comment

* add export

Make CTC align op support for empty output

disable nccl and parallel_do test

Add target assigner operator for SSD detection.

make inference_lib_dist for fluid inference shared library

adjust the structure of documentation

Fundamental Data Reading in C++

* refine get cfgs method in memory optimization transpiler

* clean code

* It will sightly faster compile and make warpctc compile
well on CUDA 9 and GCC 5.5

Impl scalar switch case op with condition op

* set up python code

* fix bug

* add cc file

* fix cmake

* add inference test for label semantic role

* fix

* address comments

* address comments

* address comments

* address comments

* add use_cuda