test=develop

* wip simplify operator framework

* wip

* wip

* done test=develop

* clean test=develop

* fix test=develop

* fix deps test=develop

* fix cpu build test=develop

* fix tensorrt build test=develop

* fix tests test=develop

* fix test=develop

* fix cpu build test=develop

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test=develop

test=develop

test=develop

* fix input<tensor>
test=develop

* fix split_ids
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* ElementwiseMul should not support SelectedRows

* fix scale op
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* change GetTensorFromVar() method to GetTensorOrSelectedRowsFromVar()

* fix operator

* refine MultiOutput

* fix MultiOutput
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* disable test_dist_save_load
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* fix elementwise_op
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* add get_sparse_as_op
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* add info for check
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* rename get_sparse_as_op with extract_rows_as_op.
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* elementwise doesn't support selected_rows

* fix regularizer

* remove extract_rows_as
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* fix ci
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* add test for sum_op

* fix regularizer
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*  test=develop

* fix pserver weight decay multi inputs test=develop

Fix code to support cpplint syntax check

test=develop

Dry run tests will skip `Op.Run` and just perform job scheduling. It helps to analysis dead lock in PE.

test=develop

1. Non utf-8 characters within comments of OPs may lead to protobuf fail to parse_from_string
2. comment out some ops which not supported on windows
3. cuda libs may not be correctly linked to target on windows

test=develop

* fix nccl2 lars dist support

* put lars in momentum op

* add tests lars

* fix ci

* fix cpu kernel

* soft warning

* remove lars in test_recognize_digits.py

* move to another op

* add file

* update api.spec test=develop

* update test=develop

* fix api.spec test=develop

* wip

* wip, finish grad merge ops

* wip, finish graph build

* wip test running

* work on 1 gpu

* workable version

* update

* fix tests

* fuse broadcast op

* fix compile failed

* refine

* add batch merge test mnist

* fix CI test=develop

* fix build

* use independent bn params for batch merge test=develop

* update api.spec

* follow comments and for test

* wip

* refine tests test=develop

* follow comments test=develop

* remove startup bn modify test=develop

* follow comments test=develop

* fix merge test=develop

test=develop

* add strategy doc
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* fix doc
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* add ParallelExecutor arg doc
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This reverts commit 21bb9e91, reversing
changes made to 3fa68dc1.

test=develop

test=develop

* hide operator API

* update

* update api.spec

* fix merge

* fix test