Use explicit specialize function

- it is better for debugging

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Added IndexDispatch and optimize #instVarAt:*

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Optimized #invokeOn:

Signed-off-by: Stefan Marr <git@stefan-marr.de>