Extracts an interface for something with a position+angle.
Adds emitters to emitters (for children emitters).
Creates an EmitterBuilder, for constructing complex scripted emitters.
Updates the engine to properly update nested emitters.
Updates the test screen with some emitter-orbiting-emitters (along with the tilemap).
Merge pull request #12 from mohammedh123/feature/emitters-orbiting-emitters

Feature/emitters orbiting emitters