* change 'math' to 'math_kernel'

* fix compile bugs

* merge develop

* fix compile bugs

* move cpu_impl of elementwise kernel to new directory

* add empty and empty_like kernel in pten

* add empty dev_api

* add pten kernel cmake

* add pten kernel cmake function

* fix compile error

* add enforce include for full kernel

* fix compile failed

* change cuda to gpu

* fix cmake function error

* add variadic_args kernel in pten

* merge develop code

* add variadic_args kernel and benchmark

* change dynamic_cast to static_cast for DeviceContext

* merge the code

* modify code format

* refactor variadic kernel function

* refine the kernel register impl

* fix cmake and symbol error

* remove overload marco

* polish details

* add code-gen file

* add api-gen in cmake

* adjust the code format

* temp save the code

* add genen-api module into pten

* merge the develop code

* fix merge conflict

* fix code conflict with develop

* support reduce_mean/sum

* fix the CI requirement

* fix requirement problem of CI

* remove original api code

* fix bug caused by removing original api