INT: added a method Engine::play() for people preferring using a Game class
INT: acces Engine::window() and Engine.inputs() to avoid having to change the cb signature all the time
INT: extracted (Triangle)Mesh to it's own header
INT: extracted the FPS counter in its own class
INT: removed the whole callback thingy and use an abstract Game class
INT: the start stop mechanics is back in the window to simplify the engine class: it's just a game loop
INT: a Game has an Engine, a Window and some Inputs ==> the car analogy
Merge branch 'master' of https://github.com/meuter/tiny