* user can call dataset.set_download_cmd to set its customized download cmd
* add UT to cover this scenario

* Add the codegen and auto fusion for sum Op  in fusion group

* Refine adam op, test=develop

* Fuse kernels together to reduce cpu time.

* Refine paddle enforce, test=develop

* Remove some comments, test=develop

* Refine code,test=develop

* Refine cuda kernel, test=develop

* Refine code according to comments, test=develop

* Correct CPU gradients of the argsort op, form a network to test its forward and backward process, test=develop

* fix dynamic threshold error in test_argsort_op, test=develop

As the title

* refine pointer and c-api prototype, test=develop

* fix new c api profile bug, test=develop

* add unit tests, test=develop

* support cond in clone, test=develop

* refine code, test=develop

* refine code, test=develop

* follow comments, test=develop

* refine code, test=develop

* add framework overhead ratio, test=develop

* print GpuMemcpy overhead, test=develop

* register fp16 for assign op, test=develop

* add op test for fp16, test=develop

* Add two types of Metric Calculator: MultiTaskCalculator & CmatchRankCalculator.
* Add a config for DynamicAdjustChannelNum function to denote whether we will discard the remaining instances when they are not be distributed evenly.
* Remove CPU code in Pull/PushSparse and we will add it back when testing it fully.
* Fix some known issues: such as copying persistable vars after one epoch running.

* add partial_sum_op, test=develop

* modify the Paddle Error Message, test=develop

* modify the Paddle Error Message, test=develop

* modify the bug for python3, test=develop

* modify the ut for ci, test=develop

* mv to contrib, test=develop

* use check_variable_and_dtype, test=develop

* fix ci, test=develop

* fix conflict, test=dvelop

* add partial concat, test=develop

* fix the conflict, test=develop

* fix the error, test=develop

* rm SSE4, test=develop

* add support for the driver api callback and fix the profiler name show bug

* add partial_concat, test=develop

* fix the grids and blocks, test=develop

* fix the Paddle_Enforce, test=develop

* fix the doc of op, test=develop

* fix the doc, test=develop

* fix the doc of the op, test=develop

* replace -1 with None, test=develop

* Add an interface of disabling FC padding
* fix bert regression
* polish fc padding interface
* recover pass function
* fix argument error
* fix mkldnn error

test=develop

* add sync communicator and implement

1. Add PADDLE_ENFORCE to Check Sequence Length of RecurrentOp.
2. Also enrich PADDLE_ENFORCE error messages.

* fix the profile print error test=develop

* improve the mul_mkldnn_op line coverage
test=develop

* remove fp32 mul mkldnn kernel
test=develop

* locally refactoring
test=develop

* change according to reviews
test=develop

* add python flag to control profile level test=develop

* fix trt log
test=develop

* fix comments
test=develop

* Add TopK Op Grad CPU&GPU Kernel test=develop

* Add TopK Op Grad, modify grad op maker test=develop

* Add TopK Op Grad, modify grad op maker test=develop

* Add TopK Op Grad, modify PADDLE_ENFORCE test=develop

* Add TopK Op Grad, modify PADDLE_THROW test=develop

* Add TopK Op Grad, modify unittest test=develop

* fix ngraph top k op unittest test=develop

* update ops's unittest of elementwise_pow, elementwise_max, elementwise_min, scale and sqrt
1. update elementwise_pow, elementwise_max and scale's unitests with input data type (float32 -> float64)
2. fix bug that the elementwise_pow doesn't meet threshold requirements with tackling float64 data
3. remove sqrt from op_accuracy_white_list.py
4. update the unittests of elementwise_pow, elementwise_max and elementwise_min ops that their input data shape over 100
5. test=develop

* modify the writing style according suggestions
test=develop