refine gc code
test=develop

* Rewrite gradient ProtoMaker for affine_channel_op to remove the Output as the input.
* Add act in Python API to make the act can be in-place by layer_help.py

remove graph visualizer tool, which can be replaced by python IrGraph draw API

Fix lod reset

Approval rd api

* temoprarily disable the code of use kCUDNN, test=develop

* add TODO comment, test=develop

fix formula in dropout

* add resnet nccl2 test=develop

* test dist train test=develop

* update test=develop

* increase timeout test=develop

* test on CI env test=develop

* Add enabling quantization

test=develop

* remove unused (here) function

fix pattern maching conv2d with(out) ResidualData

* Enhance affine_channel_op infer-shape check

* save infer model bug fix, return target vars' name list

not use PERSISTENT in batch_norm. test=develop

add runtime_context_cache_pass

* Add softmax_with_cross_entropy_op test=develop

* simplify implementation test=develop

update sqrt explaination

* fuse all_reduce
test=develop

* add fuse_parameter_groups_size
test=develop

* Polish code
test=develop

* Fix travis-ci
test=develop

* Add SetGroupAccordingToLayers and SetGroupAccordingToGroupSize
test=develop

* Add SetGroupAccordingToMemorySize
test=develop

* fix multi_devices_graph
test=develop

* reset params_grads
test=develop

* Polish code
test=develop

Remove unused variables in op grad maker

* take care edge cases test=develop

* use pragma test=develop

refine cos_sim infershape

test=develop

* wip allreduce in op

* wip

* wip

* wip

* wip adding test

* wip for conflict with mp mode

* fix tests test=develop

* fix cpu build test=develop

* fix travis clang format test=develop

* fix cpu build test=develop

* update api.spec test=develop

* delete comment test=develop

* fix cpplint test=develop

* fix test=develop

* follow comment test=develop

* add file test=develop

* fix build test=develop

* update test=develop

* to be compatible with sync_bn, and fix mp mode in develop test=develop

test=develop

test=develop

Revert "cache runtime_context"

* Make step_input support custom lod level.
test=develop

* Fix API.spec
test=develop

* Fix API.spec.
test=develop

* Fix API.spec
test=develop

* Add default value in document of step_input.
test=develop

* Fix document.
test=develop

* Fix API.spec
test=develop

test=develop

Fix concat

refine sequence enumerate op

Implement imperative infer var type