* 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

* 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

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

test=develop

* - Fix to crash of Transformer when mkldnn is to be used

Desc: TensorCopy was not setting MKLDNN primitive descriptor when layout was to be kMKLDNN

test=develop

* - Enable transformer for mkl-dnn

test=develo

* - Compilation fix

test=develop

* - Removed manual selection of MKL-DNN ops to be used in Transformer test

test=develop

test=develop

* Add cpu_quantize_placement_pass for C-API quantization

test=develop

* added a comment on required pass attributes

test=develop

cache runtime_context

test=develop

Remove const_cast in optimizers

test=develop

* Enable INT8 transpose kernel for MobileNet-SSD improvement.
test=develop

* Refine the license year.
test=develop

* Delete redundant code.
test=develop

* Add axis check.
test=develop

add more imperative layer tests.

refine fc_infershape

* update load persistables for increment, test=develop

* update load persistables for increment, test=develop

* update API Spec, test=develop

* update API Spec, test=develop

* add doc, test=develop

* add doc, test=develop

* Update lookup_table_utils.py

* Update API.spec

* Update lookup_table_utils.py

test=develop

* Update API.spec

test=develop

* fix api spec

* Update lookup_table_utils.py

test=develop

test=develop

Improve imperative mode training speed

test=develop

test=develop

test=develop

test=develop