Merge pull request #94 from videlais/master

Quadtree.js: Fixes, Docs
bring back quadtree tests
don't use deepEqual where we dont have to + fix formatting
use isDrawable instead of isImage
test prev failing load of BMPs
build
explain src/extras-dir in readme
return self in add(), load() and loadAll() for chainability
setRoot() function that sets root and returns self
test new chainabillity
test sprite.stepToWhile()
sprite.stepToWhile() - simple tweening towards x/y with collision detection callback
Rect shrink() and clonse()
seems like ff can play mp3s
fix is_ie / is_ff variables
formating
formating #2
fill(), fills screen with given color
SpriteList smart add()
test SpriteList add()