* native commit for triple grad of sigmod

* Updated unittests files

* init functional jacobian api

* Updated trible_test func

* Updated gradient_checker & test_script

* finish test with dtype float32

* add float64 test case

* polish code

* use atol=1e-5 with dtype float64

* fix for ci

* set timeout for test_jacobian

* fix dygraph grad to support high differential

* polish API docstring

* Updated gradient checker and some related files

* fix double grad strip error for high differential

* fix double grad strip error for high differential

* Add Sigmoid triple grad tests

* fix dygraph double grad dtype error when calling for high differential senario

* Updated triple grad teses func

* Use np.random to initialize ddx

* Updated triple_grad_check func

* add todo for gradient checker and refine some comments

* remove additional code

* add test for warnging in backward.py

* format python code
Co-authored-by: Nveyron95 <veyron_wu@163.com>
Co-authored-by: Nlevi131 <limaolin01@baidu.com>

Sigmoid: Out = Sigmoid(X)
SigmoidGrad: DX = DOut*(1-Out)*Out

[This Patch]
Out
DOut -> SigmoidGradGrad -> DOutNew
DDX                        DDOut

DDOut = (1-Out)*Out*DDX
DOutNew = (1-2*Out)*DOut*DDX

* add IsInitialized

* rm additional log and add tanh double grad

* rename is_initialized

* fix elugradgrad test fail and error message opt

* fix unitest,test=develop

* Update prroi_pool_op.h

fix error message

* opt message,test=develop

* fix ci fail,test=develop

fix abs double grad unittest & define the data range for the abs double grad

register log double grad kernel for cpu and cuda

add abs support double grad for the api 2.0

* set esp as 1e-6 to solve elu unitest fail,test=develop

* support elu activation double grad,test=develop

* delete the code commit in .cc,test=develop

* fix relu test unpass, test=develop

* add elu double grad kernel and unit test

* add caculate dX in elu double grad functor, test=develop

* update the commit code,test=develop