test=develop, Merge branch 'develop' of https://github.com/PaddlePaddle/Paddle into feature/imperative

fix compiler error, use len20 dataset for bert

Add simple RNN in imperative

Refine Batch Norm

test=develop

Refine nms

* fix default create_parameter dtype maching initializers test=develop

* update type check test=develop

* update test=develop

add bert analyzer test

Use malloc and free in JeMalloc

test=develop, fix/multi_output_support_imperative

test=develop

Fix nccl unittest error in debug mode

test=develop

test=develop

test=develop

test=develop

test=develop

Otherwise, some other persistable variable (like RAW type) will not be created

remove legacy WITH_DOC option

rm ngraph_operator.cc test=develop

imperative supports multi grad ops

test=develop

Performance and functional fixes to LRN

* Enable mobilenet UT in separate test class; use download cache by paddle download utility and cache unzip; and fix typo; test=develop

* Extract cache_unzipping function for reuse; format code style; test=develop

* Simplify the test code by define a combined function for both downloading and unzipping; test=develop

add trt int8 support

test=develop, refine_error_message for data type

Fix prefetch one parameter

test=develop