Headless: either untimed or via rAF.
- Update to latest coffeescript/docco
- Model: modify headless interface slightly
  - Remove headless from ctor, default to world.isHeadless
  - Ctor multiStep defaults to isHeadless
  - Fix anim headless to allow either setTimeout or request anim frame
  - Adjust Model to changes
Note: goal is to have simple parameter scans in future builds.
Merge branch 'master' into gh-pages