HOW TO : use UE4 game as a lib for other projects?

  1. Is it possible to use UE4 games as a library for other programs?
  2. For instance, I create an ios app project, and i want to link it to UE4 game. What i want to achieve is user would click a button on my app, and my UE4 game started, how can i do this?
  3. Further more thoughts : can i pack UE4 project as a library ,so i can use it’s functions in other projects on all platform?
    Any help would be appreciated!