* update readme

* test=develop

* add skip_check_grad_ci of var_conv_2d test=develop

* modify check_shape_white_list test=develop

* add mutex for trt engine
test=develop

* add the test for copy_to_cpu
test=develop

更新文档错误

* these are the revised readme/readme_cn pull-request, test=develop

* this is a readme pull request, test = develop

* these are the revised readme/readme_cn pull request,test = develop

cmake选项中添加了WITH_NCCL，显示指定是否编译NCCL的部分代码，WITH_NCCL默认打开，但如果WITH_GPU为OFF，则关闭WITH_NCCL

添加了PADDLE_WITH_NCCL定义

单机单卡能够关闭NCCL编译，多卡的话需要默认打开NCCL，如果关闭NCCL，则只能使用单卡
Co-authored-by: N石晓伟 <39303645+Shixiaowei02@users.noreply.github.com>

* Sigmoid bug fix, test=develop

* fix code format

test=develop
Co-authored-by: NManjunath Bhat <manjunathbhat9920@gmail.com>

* add hdfs ls retry time and sleep time, fix save inference
* test=develop

* fix copy table bug of lost some feasign
* test=develop

* add int16 support, test=develop

* add test, test=develop

* fix typo, test=develop

* fix dtype error in slice, test=develop

* fix chain doc, test=develop, test=document_preview

* fix bug with half communicator

* update the ut precision of pad pad2d pad_constant_like from fp32 to fp64, test=develop

* add GeneralRoleMaker which is for general usage
* test=develop

* Enable quantize to reorder to nchw as well

* Correct FC MKL-DNN input dim requirements to accept 3D

* Improve DNNL FC format, error and 3D input handling

test=develop

* Improve error checking in FC

test=develop

* Improve PADDLE_ENFORCE messages in fc-related files

* Remove data layout attribute from obligatory pass args

test=develop

* Fix message in fc_mkldnn_pass to be logically correct

test=develop

remove unnecessary template.

* add no_grad_set value check in op_test, test=develop

* update ops list, test=develop

* test=develop, fix geo Send & Init

test=develop

* remove skip_check in test_activation_mkldnn_op, test=develop

* modify lite commit id to support var_conv_2d cascade. test=develop

* modify lite commit id. test=develop

* polish backward prune, test=develop

* fix control flow op bug, test=develop

* add some unittests, test=develop

* fix unittest args, test=develop

* follow huihuang's comments, test=develop

* fix dataloader early reset bug, test=develop

* change implementation, test=develop

* fix ut, test=develop