test=develop

* add Linear layer
test=develop

* update unittest for coverage
test=develop

* remove build_once & name_scope (Conv2D)
test=develop

* fix unittest
test=develop

* Conv2DTranspose

* Conv3D & Conv3DTranspose
test=develop

* Pool2D & BatchNorm

* Embedding

* LayerNorm

* GRUUnit & NCE

* PRelu

* BilinearTensorProduct

* GroupNorm & SpectralNorm

* TreeConv
test=develop

* fix LayerNorm in transformer unnittest
test=develop

* disable LayerNorm or BatchNorm in multicard
test=develop

* refine Layer.create_parameter api
test=develop

* refine LayerNorm, remove begin_norm_axis param, add normed shape check
test=develop

* LayerNorm bug fix
test=develop

* dygraph Embedding layer use lookuptable v2
test=develop

* fix test_nce
test=develop

test=develop

* fix_norm_model_average_bug

* test=develop

* refine comment test=develop

* refine comment test=develop

fix APIs, to_variable、NCE、PRelu、softmax、rankloss for dygraph, test=document_fix, test=develop (#20142)

* fix Embedding API for dygraph, test=develop, test=document_fix

* fix dtype, test=develop, test=document_fix

* update English document, test=document_fix

* update api.spec, test=document_fix

* update api.spec, test=document_fix

* update, test=document_fix

* update norm op, test=develop, test=document_fix

* fix norm api, test=develop, test=document_fix

* opt FC

* opt rest of dygraph.nn

* new param shape check and unittest

* add kwargs for Layer

* add new set_value api

* use property decorator

* update API.spec, test=develop

* use UserList, separate gettersetters, test=develop

* update test_custom_layer_with_kwargs, test=develop

* fix UserList compatibility, test=develop

* fix UserList compatibility, test=develop

* keep FC._w, test=develop

* add unittests, Conv3D bug fix, test=develop

* clean code, test=develop

* fix dygraph guard in unittest, test=develop

* add property setters, remove unused param in tracer, test=develop

* tracer none check, test=develop

* merge, test=develop

* refine, test=develop

* bug fix in  prelu and conv3d_transpose, test=develop

* rm __set__, test=develop

* set tensor value instead of assign op

* fix property setter call, test=develop

* fix api.spec, test=develop

* fix doc sample, test=develop

* update dygraph api-doc and backward api-doc, test=develop

* update dygraph api-doc and backward api-doc, update api.spec, test=develop

* update dygraph api-doc and backward api-doc, update api.spec, test=develop

* update API.spec, test=develop

* delete useless raw variables in Conv2D, test=develop

* adjust the vars number in test_graph_wrapper to pass unittest, test=develop

* fix batchnorm api param: data_layout

* fix batchnorm data_layout param; test=develop

* fix con2d transpose bias by create and init it in build_onee

* fix API spec

* test=develop, invoke ci

* fix bias_attr and act has no effect error on layer norm, conv2dTranpose, billinearTensorProduct, sequece_conv. fix original_mode not used error on GRUunit. fix sample_weight not set error on NCE. Add ut for all thoese layer

* test=develop, change success standard for conv2dTranspose

* test=develop, fix test_layers to invoke some error branch

* test=develop, fix sample code

* test=develop, fix BilinearTensorProduct failed in dygraph mode

* test=develop, fix test_layers segment fault error

* add default getItem

* test=develop, fix has_attr disabled error in Layer

* test=develop, fix GroupNorm and deepcf bug on attrs

Fix dygraph show style for FluidDoc.

fix doc: conv3d, layer norm, bilineartensorproduct, conv2dtranspose, conv3dtranspose,rowconv, groupnorm, spectralnorm, treeconv

hidden api: sequenceConv

* add api commet; test=develop

* fix fc dtype bug; test=develop

* remove float32 in default parameter; test=develop

* fix exmpale bug; test=develop

* fix build once; test=develop

* fix num_chanels bug; test=develop

* fix install check failed bug; test=develop

* WIP

* WIP

* test=develop, add api doc and example code for dygraph

* add import, test=develop

* fix fill_constant

* fix deconv

* add trainable_statist for bn in dygraph

* test=develop, fix con2d with no bias

* test=develop, fix conv_2d with no bias will have null shape

test=develop

* test=develop, add FC and test

* test=develop, refine code

* test=develop, add some Layers and tests

* test=develop, add more layers

* test=develop, add more layers

* test=develop, add force cpu option

* Update test_layers.py

remove pdb

* test=develop, refine code

* add layer norm to Layers, add transformer prepare encoding

* little change

* finish encoder part

* add decoder part

* finish model part

* add test case and part of data feed

* add transformer test

* add to_parameter, add remove in set_attr

* test=develop, fix pos encoding bug, create_parameter with stantard name

* test=develop, rm dropout test in imperative

* test=develop, fix cpu error

* test=develop, fix minize bug

* test=develop, fix one hot not stop gradient

* test=develop, fix one hot not stop gradient

* test=develop, refine parameter name

* test=develop, fix transformer test in imperative mode

* test=develop, fix transformer test in imperative mode

* test=develop, fix boost and mkl download error

* test=develop, fix boost and mkl download error

* test=develop, fix ci and refine code

* test=develop, fix ci and refine code