Semblance of structure.

Slowly forming engine concepts in my head. Goal is to have big manager
classes like Game, to control all the other classes, and middle-layer
classes to handle the nitty-gritty of doing menial tasks like creating a
sprite, then manually-scripted Screen objects that use those
middle-layer classes to slap together a playable environment.
(P.S. I can't fucking figure out how to access the viewport dimensions.
No idea why setting an image size equal to the viewport size doesn't
fill the viewport with the image.)