fixedToCamera now works across all display objects. When enabled it will fix at its current x/y coordinate, but can be changed via cameraOffset.
fixedToCamrea now works for Groups as well :) You can fix a Group to the camera and it will influence its children.
Also fixed the issue with World.preUpdate/postUpdate not being called and various small documentation issues.
New build files
Added Spring class. Fixed reason why World wasn't pre and post updating (Stage didn't have an exists property).