add linspace op

* Enable INT8 Concat Kernel to improve the performance of MobileNet-SSD.
test=develop

* Optimize UT format.
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* Fix UT file address issue.
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* Refine the license year.
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* Optimize code for new API.
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* Restructure INT8 Concat kernel.
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* refine parallelExecutor
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* Polish op_handle
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* Remove unnecessary op_handle
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* Fix Travis CI
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* Fix fetch bug
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* Remove WaitInputVarGenerated

* Fix OpHandleBase::Run
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* debug
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* use origin fetch_op_handle
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* Revert op_handle_base.cc
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* Polish code
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* Fix OpHandleBase::Run
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* code refine

* test CI and CE
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* fix OpHandle::Run
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* refine AllReduceOpHandle
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* Polish code
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* refine fused_all_reduce_op

* add unit test in test_parallel_executor_seresnext
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* 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

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

* add TODO comment, test=develop

* Add enabling quantization

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* remove unused (here) function

* Enhance affine_channel_op infer-shape check

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

* Add softmax_with_cross_entropy_op test=develop

* simplify implementation test=develop

* fuse all_reduce
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* add fuse_parameter_groups_size
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* Polish code
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* Fix travis-ci
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* Add SetGroupAccordingToLayers and SetGroupAccordingToGroupSize
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* Add SetGroupAccordingToMemorySize
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* fix multi_devices_graph
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* reset params_grads
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* Polish code
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* take care edge cases test=develop

* use pragma test=develop

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* 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

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* Make step_input support custom lod level.
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* Fix API.spec
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* Fix API.spec.
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* Fix API.spec
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* Add default value in document of step_input.
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* Fix document.
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* Fix API.spec
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