* improve the doc of data feeder related APIs (#20515)

* improve data feeder related API

* fix doc of default_main_program, multiprocess_reader (#20536)

* fix doc of default_main_program, multiprocess_reader

* update API.spec

* fix comment

* update data feeder API sample, change fluid.layers.data to fluid.data (#20568)

* update data feeder API sample, fluid.layers.data => fluid.data

* update API.spec

* update API.spec

* fix en doc train_from_dataset and infer_from_datatset
* test=document_fix

test=develop
test=release/1.6
test=document_fix

Fix api doc example bug and polish square doc (#20491)

test=develop
test=document_fix

* Refine topk stack squeeze api en doc

test=develop
test=document_fix

* refine api.spec and returns

test=develop
test=document_fix
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

test=develop
test=document_fix

* Refine StaticRNN api-doc-en

* refine static rnn doc

* refine api doc of fluid.data

* refine api doc from commends

* refine api.spec

* Refine grammer

* fix doc,  updates API documents of uniform_random and  uniform_random_batch_size_like (#20316)

*  fix doc, updates document of sequence_softmax, sequence_scatter, sequence_unpad (#20269)

Refine the en api doc of ones, zeros, reverse, assign, increment, hsigmoid and create_py_reader_by_data ops (#20343) (#20563)

test=develop, test=release/1.6, test=document_fix

* refine the en api doc of ones, zeros, reverse, increment, hsigmoid and create_py_reader_by_data ops
test=develop, test=document_preview, test=document_fix

* refine eng doc for hsigmoid and create_py_reader_by_data ops
test=develop, test=document_preview, test=document_fix

* update API.spec
test=document_fix

* Fix the parameter name axis of reverse op in eng doc
test=develop, test=document_fix

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

* Refine eng doc of zeros, ones, reverse and assign op
test=develop, test=document_fix

* Update API.spec for assign, ones, zeros and reverse
test=develop, test=document_fix

* Fix data type of reverse op in eng doc
test=develop, test=document_fix

* Update API.spec for reverse op
test=develop, test=document_fix

* Fix ErrorClipByValue, GradientClipByGlobalNorm, GradientClipByValue

* add API.spec

test=develop, test=release/1.6, test=document_fix

* refine eng doc for hard_sigmoid op
test=develop
test=document_fix

* refine the description of hard_sigmoid
 test=develop
test=document_fix

* update API.spec
test=document_fix

* Refine the decription of parameters of HardSigmoid op
test=develop, test=document_fix

* Update API.spec for hard_sigmoid op
test=develop, test=document_fix

* fix elementwise floordiv mod; test=develop

* restore nn.py; test=release/1.6

* change floordiv, mod  doc; test=release/1.6

* fix APIs: relu, relu6, hash

test=develop
test=document_fix

* fix relu6 doc

test=develop
test=document_fix

* fix API.spec

test=develop
test=document_fix

* add description link for hash

test=develop
test=document_fix

[cherry-pick] add input type and dtype check for  elu_op (#20106) fix GradientClipByNorm english doc (#20224) (#20457)

* fix GradientClipByNorm english doc (#20224)

* fix GradientClipByNorm english doc
test=develop
test=document_fix

* add input type and dtype check for  elu_op (#20106)

* elu input check
test=develop

* test=develop

* Polish En doc for some APIs
* Update some comments and API.spec

* fix APIs: cast, concat, tensor_array_to_tensor, argmin, argmax, argsort

test=develop
test=document_fix

* fix API:cos, exp, ceil, elu, brelu English doc
test=develop
test=document_fix

* Fix api docs. test=document-fix

* Fix en docs. test=develop

* Fix the doc of dynamic_gru. test=document_fix

* Update API.spec. test=document_fix

* Fix codestyle test=develop, test=document_fix

test=document_fix

* fix Print, is_empty, read_file test=document_fix

test=develop
test=release/1.6
test=document_fix

* Fix transpiler en doc (#20149)

* test=develop,test=document_fix,fix transpiler doc,add API.spec

* test=develop,test=document_fix,fix transpiler doc,add API.spec

cherry pick 91693b9c and resolve conflict in API.spec, test=document_fix (#20477)

modify en api doc

- leaky_relu
- less_than 
- log
- logical_and
- logical_or
- logical_xor
- logical_not

[cherry-pick] Polish en doc of LoDTensorArray, test=document_fix, test=release/1.6 (#19972) (#20426)

* fix some en doc test=develop test=document_fix

* fix new fluid.data API.spec test=develop test=document_fix

* fix typo test=develop, test=document_fix

* fix typo test=develop test=document_fix

* fix typo test=develop test=document_fix

* fix test=develop test=document_fix

* fix according review test=develop test=document_fix

* fix review test=develop test=document_fix

* fix according review advice test=develop test=document_fix

* fix the doc  test=develop test=document_fix

* fix API.spec test=develop test=document_fix

Modify doc for shuffle, firstn, save_vars, load_vars, L1DecayRegularizer, L2DecayRegularizer (#20287) (#20470)

* modify shuffle, firstn, regularizer, load_vars, save_vars, test=develop, test=document_fix

* test=document_fix, test=release/1.6, refine en doc (#20317)

* test=develop, fix docker with paddle nccl problem

* test=develop, refine en_doc for Variable and Program

* test=document_fix, fix English doc for Variable and Program

* test=document_fix, refine astype code block style

* test=document_fix, add example code for Variable properties

* test=release/1.6, test=document_fix, Refine en doc (#20409)

* test=develop, fix docker with paddle nccl problem

* test=develop, refine en_doc for Variable and Program

* test=document_fix, fix English doc for Variable and Program

* test=document_fix, refine astype code block style

* test=document_fix, add example code for Variable properties

* test=document_fix, fix BackwardStrategy English Doc

* test=document_fix, fix syntax

* test=document_fix, refresh API.spec

* test=document_fix, refine api spec

* test=document_fix, refine api spec

* test=release/1.6, test=document_fix, remove useless files

Cherrypick  en doc: reorder_lod_tensor_by_rank , map_reader, WeightNormParamAttr, io.compose  (#20463)

* modify map_reader en doc (#20229)

* modify WeightNormParamAttr en doc (#20218)

* modify reorder_lod_tensor_by_rank en doc

* modify compose en doc (#20217)

update the api doc of BuildStrategy and its settings

refine en api doc of [shape, scale, split, selu, soft_relu, scatter], test=develop, test=document_fix (#20264) (#20458)

* add new save load interface; test=develop

* add new save interface; test=develop

* add save load interface ;

* fix save load error;

* fix dygraph set dict bug;

* add save load unit test; test=develop

* fix test_imperative_optimizer bug; test=develop

* fix unitest optimizer bug; test=develop

* fix code coverage; test=develop

* fix converage; test=develop

* add document for apis; test=develop

* fix unitest error; test=develop

* fix save load unit test error; test=develop

* fix error message; test=develop

* change set_parameter set_optimizer to save_dygraph; test=develop

* add load_graph check; test=develop

* fix api spec; test=develop