small documentation fixes
moved the 'updateNativeOverlay' code into the 'onEnterFrame' callback

That way, the overlay has the correct size even before you call "start" on Starling. That's useful when using the conventional display list e.g. for the loading screen.
avoiding two more 'push' calls (closes #651)
avoiding push
for consistency, 'tint' is the only function that does not return 'this'.
empty TextField fix