* open header for custom kernel

* add core utils

* tidy core code

* tify header

* tidy include

* tidy namespace

* resolve conflit

* fix unittest and coverage

* remove platform using

* resolve conflict

* resolve conflict

* fix digamma namespace error

* fix xpu full kernel error

* fix xpu full kernel error

* polish details

* add place for lib storage

* transfer: string tinyformat errors and part of enforce into pten

* remove comment

* fix by code review

* assert is not compile in -DNDEBUG

* add string as dependences of paddle_inference