Improved performance of bitmap filters by 2x

This only works with the latest dart2js compiler which inlines the
shift-right operator if the left operator is known to be a positive 32
bit integer.
Same as last change list, but other dart2js hint.
Optimized the Tween class
Added AnimationGroup and AnimationChain
Added convenience methods to Juggler.

addChain -> AnimationChain
addGroup -> AnimationGroup
Minor update to AnimationGroup/AnimationChain
Better documentation for juggler framework.
Transition implements (not extends) Animatable
Fixed documentation of Tween
More Juggler Framework documentation.
Added HtmlObject
fixed typo in HtmlObject documentation
Fixed HtmlObject visible property
Improved HtmlObject visibility control
fixed typo in AnimationChain documentation
EventDispatcher.removeEventListener and untitest

This is work done by Michael Randolph
https://github.com/mrand01/StageXL
Fixed vector test in JavaScript
Added EventStreamSubscription priorities.
Fixed BroadcastEvents
Added userData property to DisplayObject.