This PR makes assign op support LoDTensorArray and enable the loop_vars in
while_loop to support tuple or list.

* Add weight quantization in post_training_quanzitaion (#22445)

* [cherry-pick]Support int16 for Tensor (#22423)

* add int16 support, test=develop, test=release/1.7
Co-authored-by: NLeo Chen <chenqiuliang@baidu.com>

add cp27-cp27m-gcc82 and cp27-cp27mu-gcc82 branch to support gcc8.2 compile for paddle, test=develop (#22504) (#22524)

[cherry-pick] #22509

支持不依赖nccl进行编译。

多卡下，如果没有打开WITH_NCCL开关编译，多卡不能通信，则只能选择一张卡使用

[cherry-pick] #22484

支持不依赖nccl进行编译。

多卡下，如果没有打开WITH_NCCL开关编译，则只能使用单卡

test=develop

* optimize interpolate op.
test=develop

test=release/1.7

* Add dequant scale squash

* Correct dequant-scale squash test

test=release/1.7

* R-language inference support

* change pslib url of release1.7 to a stable commit
* test=develop

* revised readme/readme_cn for paddle (#22219)

* 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

* revised version 1.6.2->1.6.3,test=release/1.7

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

[cherry-pick] #22384 and #22371

22384增加了WITH_NCCL开关

22371修改了fluid依赖lite的commit id

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

* Fix GEO-SGD init & send Bug (#22375)

* test=develop, fix geo Send & Init

* test=release/1.7,test=develop, cherry-pick 8f36c395

* fix copy table bug (#22432)

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

* add hdfs ls retry time and sleep time, fix save inference (#22433)

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

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

* add collective communication library in fleet to replace mpi
* test=develop

test=release/1.7

* 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

* Improve error checking in FC

* Improve PADDLE_ENFORCE messages in fc-related files

* Remove data layout attribute from obligatory pass args

* Fix message in fc_mkldnn_pass to be logically correct

* fix bug with half communicator

test=release/1.7, test=develop

* add half_async in the communicator
* fix DistributedStrategy

* add multiprocess for dygraph data loader, test=develop

* polish code & add safe gurad, test=develop

* refactor dygraph dataloader & add signal handler, test=develop

* fix member initializer compile error on ci, test=develop

* fix member initializer compile error one more, test=develop

* remove useless config, test=develop

* skip windows incompatible problem, test=develop

* add unittest for coverage, test=coverage

* add more exception unittest case, test=develop

* deal with signal handler coverage, test=develop

* polish code & add signal handler tests, test=develop

* deal with coverage ci problem, test=develop

* split data loader test & coverage ci fix, test=develop

* remove test_imperative_data_loader_with_exception, test=develop

* remove singal process except test case, test=develop

* add exception tests again & remove sample list test, test=develop

* split normal and exception unittests to diff class, test=develop

* polish doc for use_multiprocess effect in static mode, test=develop

* cherry-pick fix dataloader early reset bug, test=release/1.7

* cherry-pick implementation changing, test=release/1.7

* fix ut, test=release/1.7

test=release/1.7, test=develop

* add learning rate api; test=develop

* fix uni test converage; test=develop

* fix travis ci error; test=develop

* fix comment; test=develop

* fix example error; test=develop

* polish the api description, test=develop
Co-authored-by: Nzhongpu <2013000149@qq.com>
Co-authored-by: Nhong <43953930+phlrain@users.noreply.github.com>

* add parameter check; test=develop

* change parameter name checker in dygraph guard; test=develop

* fix test layers error; test=develop

* revert some code to develop; test=develop

* fix exampel error; test=develop

* fix comment error; test=develop

* fix comment error; test=develop