refine dataset API

Add async ssa graph executor communicator

test=develop

Check default grad op maker revision

* add seresnet unittest test=develop

* add dropout layer test=develop

* fix ci test=develop

* fix comment test=develop

* fix comment test=develop

* fix ci test=develop

* fix ci test=develop

* fix ci

* fix module name test=develop

* run imperative serenext unit test serially test=develop

test=develop

test=develop

test=develop

merge feature/anakin-engine to develop

Merge branch 'develop' of https://github.com/PaddlePaddle/Paddle into add-async-ssa-graph-executor-communicator
test=develop

Train with pipe reader merge develop

Merge branch 'develop' of https://github.com/PaddlePaddle/Paddle into add-async-ssa-graph-executor-communicator
test=develop

Support imperative learning rate scheduler

* Add linear learning warmup method

This warmup lr can be combinated with other learning rate strategies.
For example:
            decayed_lr = fluid.layers.linear_lr_warmup(
                fluid.layers.piecewise_decay(boundaries, lr_steps),
                warmup_steps, start_lr, end_lr)

* fix cudnn batch norm accuracy test=develop

* fix cudnn batch norm accuracy test=develop

* disable failed test for later fix test=develop

test=develop

Fix document array_read code error

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

remove the useless check 

* fix compiled
test=develop

* follow comments test=develop

test=develop

KL div loss: add kldiv_loss op

Add attr 'axis' for softmax

Add temporal_shift op for TSM model

* Add DecoupledWeightDecay

remove profiling from int8 analyzer test