* refine recurrent_op
test=develop

* remove unnecessary code
test=develop

refine embeddingseqpool grad

* In some case, the input may have one than one negative value.
test=develop

* fix matmul bug
test=develop

* test=develop, reconstruct layer helper to fit imperative usage

* test=develop, fix import error on py35

* test=develop, fix rnn gradient error

* test=develop, delete test use code

* test=develop, remove helper from imperative usage

* test=develop, fix test_base_layer using new helper

* test=develop, reconstruct layerhelper for imperative mode

* test=develop, reconstruct layerhelper for imperative mode

* test=develop, fix bug

* test=develop, fix test failed bug

* test=develop, fix test failed bug

* test=develop, fix test failed bug

* test=develop, fix bug

* test=develop, polish code

refine SetCpuMathLibraryNumThreads

* remove the ignored from is_empty and less_than test=develop

* fix api spec test=develop

* fix the api spec test=develop

* test=develop

* unified PE and compiler
test=develop

* Polish code
test=develop

remove legacy function in ExecutionContext

Add spectral norm op

* add ir memory optimize test case for IfElse op, test=develop

* fix some unitttest failure by force using the python memory_optimize, test=develop

* tweak comments, test=develop

* fix unittest, test=develop

* fix unittest, test=develop

test=develop

test=develop

test=develop

test=develop

* MKLDNN: Add UT for conv_transpose_mkldnn op.
test=develop

* MKLDNN: Add fuse_bias check UT for conv_transpose_mkldnn op.
test=develop

Fix doc md5

test=develop

* Revert "Add Event for TensorCopy (#15953)"

This reverts commit 7235fd66.
test=develop

* fix CI
test=develop

Fix develop Executor doc

test=develop

* Update detection API add new check document

* update API.spec

* test=develop;add shanyi15 approved API.spec

* test=develop;update PM check API.spec

* check api.spec

* test=develop

* update API.spec

* test=develop;update API.spec

* update API.spec

* cat API.spec

* update documnent in api.spec

* check python35 api.spec

* update print_signatures md5 function

* test=develop

* update API.spec

* test=develop;fix python3 API.spec diff

* test=develop

* test=develop

* test=develop

MKL-DNN: Add a unit test for pooling when ceil mode is enabled

* Unified ParallelExecutor and Compiler