* Add lookahead optimizer

* add unittest for lookahead optimizer

test=develop

* add doc string for LookaheadOptimizer

test=develop
test=document_preview

* add API spec for lookahead

test=develop
test=document_preview

* modify api spec

test=develop
test=document_preview

* modified doc string

* modify the test file

test=develop
test=document_preview

* modify doc string

test=develop
test=document_preview

* test=develop,Optimized error reporting information

* test=develop,add importscipy unittest

* test=develop, rename the file and function

* add default getItem

* test=develop, fix has_attr disabled error in Layer

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

* fix sync mode hang in transpiler
* remove sync mode in send/recv
* replace PADDLE_ENFORCE with PADDLE_ENFORCE_NE

* Fix arg do_model_average in param_attr

test=develop

* Update api spec

test=develop

 add fleet_desc config feature & multi_sparse table,

* update light_nas_strategy: add latency constraint

test=develop

* update light_nas_strategy: update get_model_latency

test=develop

* update light_nas_strategy: add more check

test=develop

* update light_nas test

test=develop

* update light_nas test

    test=develop

* minor update light_nas test

    test=develop

* minor update light_nas test

test=develop

* update light_nas test

test=develop

* update _constrain_func of light_nas_strategy

test=develop

* update _constrain_func of light_nas_strategy

test=develop

* remove unused code

test=develop

* add pool2d quantization support, only for max-pooling.

* add the partial quantization support.

* Fix data parallel & sequence mask in dygraph

test=develop

* Revert change in data_parallel

test=develop

* use PE for compiler
test=develop

* Implement the operator with sprase matrix multiply

* Update the URL of mklml library.

test=develop

* Disable MKLML implematation when using no-linux.

test=develop

* optimize bp with mkl sparse matrix
test=develop

* add pybind interface to get all inplace ops, test=develop

* enhance OpTest to check whether the consistency of operator when using and not using inplace, test=develop

* handle corner cases in op_test, test=develop

* support outputs without tensor holder_, like XShape in reshape_op, test=develop

* fix bug, some op has GradOpMaker, but actually no grad_op in OpInfoMap, test=develop

* use reshape_grad instead of reshape in FlattenGradOp, test=develop

* fix error debug dims info for variables like XShape, test=develop

* change computational order in sum_op to relieve computation difference using inplace, test=develop

* add inplace_atol to check group_norm, and skip inplace_grad for mkldnn, test=develop

* follow sneaxiy's comments, test=develop

* remove unused DefaultGradOpDescMaker in mkldnn op, test=develop

* add diag init in Uniform_random op test=develop

* modify api.spec test=develop

* fix unform_batch_size_like maker test=develop

* add diag_num and diag_step assert check test=develop

* update parallel.py
test=develop

* increase test_parallel_executor_seresnext time limit
test=develop

* split test_parallel_executor_seresnext
test=develop

* temporally disable reduce_and_allreduce test because of the random failure.
test=develop

* split gpu and cpu
test=develop

* add elementwise_mul_mkldnn UT with [conv + elt_mul + conv] to cover avx512=True branch
test=develop

* change a typo.
test=develop

test=develop, test=document_preview

distribute launch : add use_paddlecloud argument 

* fix mask rcnn bug:
1. affine channel fuse (diff)
2. condition block op (memory leak)
3. merge lod tensor op (diff)
4. memroy optim (diff)
test=develop

* fix ci aboud PADDLE_ENFOCE
fix merge lod infer op ut
test=develop

* add matrch_matrix_tensor op test=develop

* fix ignore unittest if with_mkl=off test=develop

* clean code and rm is_test param test=develop

* modify API.spec test=develop

* rm useless code in search_compute.h test=develop

* modify api.spec test=develop

* modify default_grad.spec test=develop

* Add API test code test=develop

* clean code in search_computer.h

* modify PADDLE_ENFORCE and clean search_compute.h test=develop

* fix code style test=develop

add fl_listen_and_serv op for Federated_learning and fl_distribute_transpiler add this op to pserver program . This op just listen the endpoint and sum&scale.

add python coverage launch when WITH_COVERAGE=ON

* fix REGISTER_OP_WITHOUT_GRADIENT
test=develop

Unset unittests http_proxy env to avoid timeout.

* imporve the doc of decorate_reader API, test=develop

* udpate API.spec, test=develop

node_num is not needed for users, so remove them and fix the bugs about it!

* remove unused inference_transpiler unit-tests

test=develop

* remove InferenceTranspiler usage in quantize_transpiler.py

test=develop

* Fix recurrent op fails

For the variable used in outter block,
copy sub block's grad variable to outter block

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

* Fix unicode error

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

* Refine test code

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

* Fix seq2seq case fails

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

* remove unreasonable code.

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

* Refine code according to comment

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

* add exception exit on error example codes test=develop

test=develop

* Add padding support for crf_decoding

* Fixes in comupte kernel

test=develop

* Update API Spec

test=develop

* Update API.spec

test=develop

* Avoid using paddle_enforce

test=develop

* Fix enforce

test=develop

Remove is_test parameter of FC op. The parameter is_test is not used anywhere.

* change the default value of summarize from -1 to 20 in Print op to improve ease of use, test=develop

* change the doc of API Print to make the document easier to understand, test=develop