Python examples of fluid.layers.io.double_buffer and some BuildStrategy's methods.

* add conv_concat_relu fuse

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* add test code

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* added missing include with unordered_map

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* review fixes for wojtuss

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* remove 'should (not) be fused' comment statements

one of them was invalid anyway

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* fix quantize_squash_pass segfault when there is no tensor linked do Bias input

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* add googlenet test

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* fix concat CreateKey not using input format

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* add profiler in tracer.cc

* add profiler in layer.cc
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* add profiler in Layer.cc
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* test=develop

* test=develop

* test=develop

* del #

*  Enable assign operator for a ngraph, test=develop

* Cross_entropy operators needs to be updated

* polish_executor_and_add_ctx_cache

* refine softmax fwd

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* refine cpu softmax bwd

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* fix batch size

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* fix compile issue with gpu

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* add value clip

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* Add exponential moving average

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* Polish documents

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* Update API spec

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* refine softmax fwd

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* fix compile issue wih gpu

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* add value clip to avoid exp

* Revert "Revert "Fix allocator bug""

This reverts commit 174d0d0b.

* Revert "fix travis ci"

This reverts commit 5656fa9f.

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* add inlined_vector.h, test=develop

* add inlined_vector_test,test=develop

* test=develop

* test=develop

* fix api example. test=develop

* fix API.spec. test=develop

* fix spectral_norm format. test=develpp

* merge develop

* add import. test=develop

* fix indent. test=develop

* fix indent. test=develop

* add import fluid. test=develop

* fix distribute doc

* fix concat op vartype check, test=develop

Async exe support communicator

ban all trt ut. will fix it later.

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* fix bpr data_norm teacher_student_sigmoid , test=develop test=document_preview

修复了bpr_loss data_norm teacher_student_sigmoid_loss三个api, 同时修复了continuous_value_model文档英文拼写错误

* fix api doc according to the reviewer's comment test=develop

* test=develop

* test=develop

* modify saved model path in analyzer_save_model.cc test=develop

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* test=develop, fix con2d with no bias

* test=develop, fix conv_2d with no bias will have null shape

* add increment op to ngraph engine

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* fix style errors

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* Fix examples of fluid.layers.sums.
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* Correct the example of DynamicRNN and its functions.
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* Add 'import paddle.fluid as fluid' to examples.
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* Update API.spec.
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* Add space lines.
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* Update the API.spec.
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* Relu6 is the bottleneck op for Mobilenet-v2. As the mkldnn supports the conv/relu6 fusion, we implement it fusion via cpass way. Due to the int8 enabling for this fusion will be supported in MKLDNN v0.20, so this PR is focused on the fp32 optimization.

Below table shows the benchmark(FPS) which measured on skx-8180(28 cores)
Batch size | with fusion | without fusion
-- | -- | --
1 | 214.7 | 53.4
50 | 1219.727 | 137.280

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* Fix the format issue

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* Add the missing nolint comments.

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* Fix the typos.

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* Register the conv_brelu_mkldnn_fuse_pass for the MKLDNN engine.

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* Adjust the indentation.

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* Add the test_conv_brelu_mkldnn_fuse_pass case.

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* Slightly update the code per Baidu comments.
Let the parameter definition embedded into the code.
That's will make the code easy to understand.

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* add quant_dequant_pass, test=develop

* Add quant_dequant before some ops, such as the elementwise_add op. This is required by TensorRT. test=develop

* Add LAMB optimizer

* Expose LAMB Optimizer's APIs

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* Cleanup code & doc

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* Update lamb optimizer's formula

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