* Layer add training attr, add Dropout Layer

* add unit test for Dropout
test=develop

* minor fix
test=develop

* add missing args
test=develop

* support global flag in dropout, add docs
test=develop

* minor fix
test=develop

* minor fix
test=develop

* refine code comments
test=develop

* refine Dropout
test=develop

* fix ut
test=develop

* arg expansion
test=develop

* sample code update
test=develop

* prop -> p
test=develop

* fix ut
test=develop

* minor check fix
test=develop

* add inplace_abn_op. test=develop

test=develop

test=develop

* dygraph support cond op
test=develop

* unittest coverage
test=develop

* fix coverage
test=develop

* fix for coverage
test=develop

* refine TypeError msg
test=develop

* remove restrict
test=develop

* dygraph support while_loop op
test=develop

* refine assign
test=develop

* add partial_sum_op, test=develop

* modify the Paddle Error Message, test=develop

* modify the Paddle Error Message, test=develop

* modify the bug for python3, test=develop

* modify the ut for ci, test=develop

* mv to contrib, test=develop

* use check_variable_and_dtype, test=develop

* fix ci, test=develop

* fix conflict, test=dvelop

* add partial concat, test=develop

* fix the conflict, test=develop

* fix the error, test=develop

* rm SSE4, test=develop

* add partial_concat, test=develop

* fix the grids and blocks, test=develop

* fix the Paddle_Enforce, test=develop

* fix the doc of op, test=develop

* fix the doc, test=develop

* fix the doc of the op, test=develop

* replace -1 with None, test=develop

* fix test_layers compare static graph and dygraph result; test=develop

* fix test_layers random error; test=develop

* 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

* update PRelu arg
test=develop

* fix unittests
test=develop

* fix element mode alpha shape
test=develop

* split channel_or_input_shape arg
test=develop

* fix unittest
test=develop

* modify fc to linear in sample code, test=develop

* remove FC, test=develop

* remove warnings, test=develop

* drop fluid/imperative/README.md , test=develop

* change fc to linear, test=develop

* polish code style, test=develop

* convert dtype of vars for range op, test=develop

* move private weight properties to public ones
test=develop

* revert changes to FC
test=develop

* fix unittest
test=develop

* fix unittest
test=develop

* fix coverage
test=develop

* fix merged dev
test=develop

* bug fix
test=develop

* update layers used in mnist dygraph model, test=develop

* fix import issue, test=develop

* add dygraph utils, test=develop

* add unittest, test=develop

* add shuffle batch op, test=develop, test=document_preview

* fix size_t conflict and check_output test=develop, test=document_preview

* fix bug test=develop, test=document_preview

* add unittest of shuffle_batch layer test=develop, test=document_preview

* fix py coverage and op input type, test=develop, test=document_preview

* fix py coverage, test=develop

* fix en doc, test=develop

* move to contrib test=develop

* add unique_name test=develop

* invoke shuffle_batch in contrib.layers test=develop

* remove params in Tracer object, test=develop

* Repair failed optest, 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

* fix optest,test=develop

* fix optest, test=develop

* fix optest for pass parameter_list when constructing an Optimizer class instance, test=develop

* polish code for better code style, test=develop

* fix se_resnext optest, test=develop

* polish code for better code style, test=develop
Co-authored-by: Nsongyouwei <youwei0314@gmail.com>

* update layers, test=develop

* fix input numpy, test=develop

* fix bugs, test=develop

* follow commments, test=develop

* update getitem, 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

* fix fill_constant_batch_size_like_op precious problem  test=develop

This reverts commit 007c9975.

* add Adam beta1/beta2 support Variable. test=develop

* batch_norm momentum support variable. test=develop

* fix format. test=develop

* add batch_norm momentum variable example. test=develop

* move MomentumTensor to training branch. test=develop

* split example. test=develop

* fix doc. test=develop

* fix PADDLE_ENFORCE ci. test=develop

* fix format. 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 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

* Update crf_decoding api & example

test=develop

* Update api spec

test=develop

* Fix linear chain crf api

test=develop

* Avoid sharing data pointer with input

test=develop

* Simplify the logic in linear_chain_crf_decoding

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

test=develop

* Update API spec

test=develop

* Add unittest for layers && correct infer_shape in chunk_eval

test=develop

* 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

* 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, add compat test and fix inplace campat dict error

* fix pool infershape. test=develop

* fix unittest converage. test=develop

* fix format. test=develop

* Removing last dims constraints of seq_pad and seq_unpad test=develop

* fix test_layer api code test=develop

* fix sequence_pad_op.cc conflict test=develop

* remove test_analyzer_mm_dnn test=develop

* fix vectorize bug test=develop

* fix vectorize<int> test=develop

* add mse_loss op

* move tree_conv to fluid.contrib.layers

test=develop

* update API.spec for tree_conv

test=develop

* update tree_conv api to increase unit coverage

test=develop