* support gradient merge with recompute, test=develop
test=develop

*test=kunlun

* modify test_load_op save path from /tmp to ./, test=develop

* trigger kunlun ci, test=kunlun

* trigger kunlun ci, test=kunlun

* update index sample

* add gather_op xpu, test=develop, test=kunlun

* fix ut, test=develop, test=kunlun

* fix the ut,test=develop, test=kunlun

* polish save load en doc details, test=document_fix

* polish details, test=document_fix

* remove blank, test=document_fix

* fix ascii error, test=document_fix

* update fc's input to x, test=document_fix

* update fc argument activation, test=document_fix

* 1. remove paddle.unique_with_counts api, which counts as unique api
2. add paddle.math.increment(x, value=1.0, name=None) api
3. replace paddle.sums with paddle.add_n api
4. update paddle.metric.accuracy api (add name parameter)

* fix doc and unittest of 2.0 lr_scheduler

* fix doc of 2.0 lr_scheduler

* fix unittest

* fix english doc of lr_scheduler

* fix api name of lr scheduler

* fix api name of lr scheduler

Update code examples for api2.0 

* remove test_lac predictor run case

* refine fleetrun.ps_launch

* update fleet run for multi device support

* ps_graph support ps-gpu

* fix heter save

* add heter save unittest

* fix unittest & simple code

* update fleetrun

* fix fleetrun

* fix launch barrier

* fix role maker

* add paddlecloud rolemaker unittest

* rename heter_worker_device_guard

* polish Return doc of DataLoader. test=develop

* mig deformable_conv to deform_conv2d

As the title

test=develop

* add load_op_xpu for Baidu Kunlun, test=kunlun

* add is_compiled_with_xpu for unit test, test=kunlun

* add is_compiled_with_xpu for unit test, test=kunlun

* refine parameters order && doc

* update rmsprop doc

* refine adam/transpose/unstack/stride_slice

* fix bug && doc

* fix doc

* bug fix

* bug fix

* fix doc

* fix doc

* fix doc

* fix doc

* depercate old strided_slice

* update doc

* set default value for name

* update doc

* fix fluid doc

* fix fluid doc

* fix fluid doc, test=document_fix

* fix fluid doc, test=document_fix

Mutiply allows non-tensor data input

* add flattern weight of lstm

* fix model bugs, inputs can be InputSpec instance

* correct error message

* Add double grad in Squeeze and Unsqueeze

* Add double grad in Squeeze and Unsqueeze

Add xpu kernel for KUNLUN core:

* accuracy op
* sign op
* scale op
* sum op

Add default atol in xpu unittest.

* Add test attribute in channelwise_quant op, test=develop

* replace config by kwargs

* change save path form dir to prefix

* fix failed unittests

* revert unittest name change

* polish en docs

* add more tests for coverage

* add matmul doublegrad op

* fix compile errors

* modify code according to review

* delete float16

* Reimplement paddle.static.nn.fc, mainly change the parameters and English documentation.

* Polish the documentation format.