* Merge branch 'develop' of https://github.com/PaddlePaddle/Paddle into api_fix

* test=release/1.6, test=document_fix

* fix en api doc test=develop test=document_fix test=document_preview

* update api.spec  test=develop test=document_fix test=document_preview

* fix some details  test=develop test=document_fix test=document_preview

* update API.spec test=document_fix test=document_preview  test=develop

* Add support for None for fluid.data (#20228)

* Refine Error Message for New Data API (#20204)

* Modify English doc of fluid.data (#20248)

* cherry pick for 131b1dc3, test=develop, test=document_fix

* cherry pick for fb21a743, test=develop, test=document_fix

[cherry-pick]fix English document of expand/pow/reshape/slice. test=release/1.6, test=document_fix (#20280) (#20356)

* fix api 1.6 doc bpr, data_norm teacher_student

* Polish english apis' doc (#20198)

* refine Normal Uniform documnet

* refine eng doc, test=release/1.6, test=document_fix

* polish en api,test=develop,test=document_fix

* modified api.spec, test=develop,test=document_fix

* modified ops for arc,test=develop,test=document_fix

* update for 1.6, test=develop,test=document_fix

* update API.spec

* Update API.spec

test=develop,test=document_fix

* Update API.spec

test=develop,test=document_fix

* refine fc/seq_conv/seq_concat en doc test=develop, test=document_fix

* refine seq_pool/reshape/reverse test=develop, test=document_fix (#20233)

* fix en_doc api of one-hot and embedding (#20187)

* Add detailed error messages for nce layer

* Fix some problems

* Fix unit test coverage

test=release/1.6

* [cherry-pick] modified doc of group_norm, test=release/1.6, test=document_fix (#20234)

* [cherry-pick] modified doc of crop_tensor, test=release/1.6, test=document_fix (#20203)

* Update apiexample (#20247), test=develop, test=document_fix

* update api example, test=develop, test=document_fix

* update api.spec, test=release/1.6, test=document_fix

test=release/1.6 test=document_fix

test=release/1.6

* fix APIs,test=develop,test=document_fix

* fix conflict, test=develop, test=document_fix

* fix confict, test=develop, test=document_fix

* fix confict, test=develop, test=document_fix

* fix API.spec, test=develop, test=document_fix

* change fluid.layers.data to fluid.data,test=develop, test=document_fix

* fix bug on example code, test=develop, test=document_fix

* fix API.spec,  test=develop, test=document_fix

* fix the error message for reduce_mean and reduce_sum op (#20063)

* fix the error message for reduce_mean and reduce_sum op test=develop

* fix typo test=develop

* fix according review advice test=develop

* fix the test test=develop

* fix test=develop

* Fill constant error message fix (#20075)

* fix the constant error message test=develop

* fix typo test=develop

* fix typo test=develop

* fix code style test=develop

* fix comment and bugs test=develop

* fix the bug test=develop

* fix and add unittest test=develop

* fix the typo test=develop

* add support for the fill_constant op test=develop

* add test for ci coverage test=develop

test=release/1.6, test=document_fix

* update en doc

* add error log

add executor.FetchHandler for train/infer from the dataset

* Speed GEO-SGD (#20158)

* delete debug vlog & add rpc function & fix word2vec bug & speed GEO-SGD

* Add lod_level parameter to paddle.fluid.data

* Add "optional" in API doc for optional parameters

Heartbeat for distributed async training.

* test=develop, fix docker with paddle nccl problem

* test=develop, Add Variable api and refine dygraph related API

* test=develop, Add Variable api and refine dygraph related API

* test=develop, refine test for new api and error info

* test=develop, refine error info and test_layers

* test=develop, add API.spec

* test=devleop, fix to_string python2 and python3 compat error and refien doc

* test=devleop, add API spec

* test=devleop, update API spec

* test=devleop, update API spec

* test=develop, invoke ci

* test=develop, fix example code

* test=develop, update API spec

* test=develop, fix auto_prune_error_on_leaf

* test=develop, fix auto prune error on loss stop_gradient

* test=develop, remove useless error check

* test=develop, add more ut for sorted gradient

* Update crf_decoding api & example

* Update api spec

* Fix linear chain crf api

* Avoid sharing data pointer with input

* Simplify the logic in linear_chain_crf_decoding

* Add unittest for crf_decoding when label & path both are set

* Update API spec

* Add unittest for layers && correct infer_shape in chunk_eval

test=release/1.6

test=release/1.6

* Add multihead op for ernie opt

* Refine softmax

* Refine kernel.

* Refine cuda kernel

* Refine cuda version

* Refine cmake

1.support asymmetric padding;
2.support padding algorithm:"SAME" and "VALID";
3.support channel_last: data_format NHWC and NDHWC;
4.change doc of python API and c++;

test=release/1.6

* refector geo sgd & communicator

* add a default value for _prune interface

* modify document