Fixes to the hero glitch:

  - fixed the random ranges so we always pick in-range
  - moved to an .onload based process — guarantees we have sometihng to work with on slow load
  - initially moved the preload, but after testing realized it wasn't actually preloading for the canvas
    so i've removed it for now. will reintroduce when i can make it more effective
Merge pull request #436 from jessevondoom/master

Fixes to the hero glitch stuff: