load_model
add scale, mul Op

* fix preprocess script with processbar, integrity check and logs
test=develop

* delete unnecessary empty lines, change function name
test=develop

enhance analyzer_tests download

* Fix bug of gradient interface

* shrink transformer

* Right transformer

* Change from width-first backward to deep-first backward process

test=develop

* Reverse iterator op's input

test=develop

* Polish code

* Change the iteration direction in ingrads' map slots

test=develop

* Polish code

test=develop

* test=develop, add FC and test

* test=develop, refine code

* fix the bug of reusing different types of variables in memory_optimize_pass, test=develop

* disable SELECTED_ROWS AND LOD_TENSOR_ARRAY reusage, test=develop

* link the libwbaes.so into paddle

* polish detail, test=develop

* try fix mac_pr_ci error, test=develop

* add compile option, test=develop

* fix ci error, test=develop

* ignore failed to find mac lib, test=develop

* change cdn to bj, cdn can't get the latest version

* trigger ci, test=develop

* temporary delete win32 lib linking, test=develop

* change https to http, test=develop

* turn compile option on to off

* turn compile option off to on, test=develop

* try lib compiled by gcc4.8, test=develop

* update lib version, test=develop

* link other lib, test=develop

* add setup config

* delete false, test=develop

* delete no_soname, test=develop

* recover so name set

* fix, test=develop

* adjust make config, test=develop

* remove link to wbaes, test=develop

* remove useless define, test=develop

refine dataset API

Add async ssa graph executor communicator

test=develop

Check default grad op maker revision

test=develop

* 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)