Rewrite entity.js, begin scene.js
More entity/scene refactoring
Rewritten vector math, render and collision modules.
Event system rewrite.

Scene now sorts entities by z-value when new entities are added.
Fixed prototype declarations for Game
Moved alien modules to alien folder.  Basic test up and running.
Entities now receive events
Decreased coupling between modules
More modularity
Drag-drop behavior added.  Currently applies to all entities on the canvas (no positional distinction)
Point in polygon collision detection for mosue event propagation
Entities can now decide whether to propagate an event or not.
Default entity properties are no longer tied to the prototype frame.  Added a canvas auto-resize to help in testing.
Game loop, canvas is only redrawn while the game is running
Entities can request not to be rendered (for key listener objects, game state objects, etc).  Space bar will start and stop the game loop via listener entity
Renderable and collidable components

Reorganized file structure a little.  Systems have their own folders now.
Basic text rendering