Change game-over logic to use exceptions
Additional helpful methods for Vector2f
Implement highlighting and selecting

Doesn't actually do anything yet, though
Add "debug mode"

Right now, all debug mode does is pause when an exception happens, so in
cases where the console window exits immediately on game unload (eg.
vim's :!cmd thingy), it will still stick around so we can see it
Add renderable text labels
Add anchor property to GameObject