* fix replicate pad when input size is 0
* add unit test

* fix pad outliers err

* fix pad api input type and doc

* fix example of pad

* add unittest for pad3d

* fix unittest

* fix error format

* fix pad doc

* add pad func

* add pad

* test=develop, add pad op and apis

* restore pad2d

* test=develop, fix paddl declare

* fix pad interface

* test=develop, fix pad

* test=develop, add all pad api and cos_sim

* test=develop, remove padding default value

* test=develop, rename var to tensor

* test=develop, add more tests

* test=develop, rename tovar to totensor

* test=develop, fix init

* test=develop, add more test

* test=develop, add more tests