* 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

* Support predictor function in JitLayer

* Pybind PEFunction

* Pybind PEFunction and call phi api in layer_test

* Call sqrt phi API

* Polish flags

* Fix comments

* [JIT]Layer support eager dygraph mode and polish Function interface

* remove usless code

* fix #define

* Pybind JitLayer VarBase Function and add python UT

* Add multi program load UT

* Fix UT place error

* Update jit.save param name

* Remove some comments

* Polish cmakelists

* Polish JitLayer in Python

* Fix comments