Main loop

[ixchow]

Currently, sald leaves the game developer to worry about creating a main loop. Let's create some reusable code which:

1. manages a <canvas> tag; including resizing the tag based on demands from the game (e.g. aspect ratio, exact size, integer multiple-of-size)
2. handles timing and drawing, passing requests to a developer-defined (and changeable) object
3. grabs input, processes it to be properly canvas-relative, and passes the results to the (developer-defined) scene object

One way we might do this is have a window.scene variable, with (optional) functions draw(), update(elapsedSeconds), key(code, state), down(x,y), motion(x,y), and up(x,y).