Stopped tiles from being drawn, getting an additional 5fps or so on my machine. Working on a new drawing API based on manual invalidation which should speed a lot of things up.
Made drawing fully recursive.
New drawing API working for Button and ToggleButton.
Made button invalidations cheaper (since they happen a lot due to bug #29)
Renamed Vector.getCenter() to the more javascripty Vector.center().
Merge pull request #90 from gitdefence/optimize

Looks good, I probably will not adopt the practice of using function calls to both set and get values, but I don't mind if you do. The changes to getCenter are fine I guess, they make it less obvious that you cannot pass in a new center, that it is a function at all, and that it is making a copy and not passing a reference... but thats okay.