* Add fsp operator.
1 Add unitest.
2. Add python API.
3. Add layer test.

* Add quantization strategy.
1. Add API.
2. Add unitest.

* Add distillatoin strategy.

* Add unitest config file for quantization

* Fix Copyright
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* Fix setup.py

* Fix document of layers.py.
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* Fix unitest in python3.
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* Fix documents.
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* 1. refine fsp op by batched gemm
2. remove unused import
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* Fix test_dist_se_resnext.
1. disable test distillation.
2. reset framework.py
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* Enable unitest of distillation after fixing Block._clone_variable
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* Fix cdn issue.
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* add launch mp distributed mode module test=develop

* delete unused file test=develop

* refine usage test=develop

* refine usage test=develop

* move distributed package test=develop

* add to whl package test=develop

* Add INT8 calibration support in Paddle package; test=develop

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* Init slim.

* Remove distillation demo.

* Fix import errors.
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* Fix some issues.
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* Fix configs.
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* Modify API.spec.
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* Fix format.
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* Fix format.
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* Add some comments.

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* fix utils config, test=develop

* reweite tools in lookup table utils, test=develop

* merge develop, test=develop

* add copy in setup, test=develop

* update api spec, test=develop

* add doc, test=develop

* prettifying doc, test=develop

* Update API.spec

update api.spec, test=develop

* Update lookup_table_utils.py

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* Update lookup_table_utils.py

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* merge develop, test=develop

* merge develop, test=develop

* init fix, test=develop

* fix in downloads, test=develop

* fix in setup.in, test=develop

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Revert "Merge pull request #14798 from PaddlePaddle/revert-14786-revert-14782-revert-14398-imperative"

This reverts commit b1d3a1c8, reversing
changes made to f1fb64b1.

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`cwd` was not set before when get commit SHA. The default `cwd` is the current build directory. However, the build directory might not be the subdirectory of source. The `git` command will fail when that happened.

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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

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* Added beam search API to fluid/contrib

* Change as review comments

* API.spec change

* Doc updated