* [JitLayer]Erase out vars to avoid data rewrittinig

* Fix code comments

* Rename class type Name2XX

* Fix return type

* Remove EngineMap function in layer

* Polish function code

* Rename funciton to engine

* Fix Log msg and doc

* Rename Function to Engine and using new Function class to warp Engine

* Rename EngineInfo

* Adjust member variable order

* Move Function classes to a sub dir

* Format code