* add expand_as op, test=develop

* add expand_as op,test=develop

* add expand_as op,test=develop

* add nn.py, test=develop

* delele paddle_enforce, test=develop

* Fix docs of gru_unit and dynamic_gru.

Fix basic_gru in rnn_impl.py.

Add error messages for param_attr setting in layer_norm api.

Add int64 dtype for expand.

test=develop

* Reopen unit-tests of basic_gru/basic_lstm in rnn_impl.py.
test=develop

* Add unit test for layer_norm api.
test=develop

* Remove the deprecated gru doc fix. test=develop

* Fix basic_gru test coverage. test=develop

* Update API.spec. test=develop

* Update API.spec. test=develop

* Fix test_basic_gru coverage test. test=develop

* Update test_basic_gru in test_layers to use fluid.data
test=develop

* Update test_basic_gru for coverage. test=develop

* Add seq2seq api related code (#19820)

* fix expand bug  (#20340)

* fix expand bug test=develop

* fix style test=develop

* fix style test=develop

* fix style test=develop

* fix style test=develop

* Fix the assign data check (#20564)

* Fix the assign data check. test=develop

* Fix test_assign_op.py. test=develop

* Update API.spec

Refine error message of transpose. fix en doc about unsqueeze, unstack, transpose, multiplex. test=develop, test=document_preview, test=document_fix (#20594)

 [Cherry-pick #20263] to Add API 'fluid.requird_version(min_version, max_version=None)' to check if the installed PaddlePaddle version is satisfied

please see #20263 for details

* 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