all "_parent" related code is refactored.
Now we have a concept "evaluator stack" system.
This system automatically passes a child evaluator to the parent when
the child complelte its task.
If your evaluator do not need to do anything after the childe complete its task
do not need to write any code.
If you want to do something after compmleting the child task (usually in evaluators which needs
to take an argument) you can write onChildComplete: method.
If you want to change the method you want to call after complete you can set XVimEvaluator's onChildCompleteHandler
to a selector you want to call.
(You can see example in "AT" method in XVimNormalEvaluator and its onComplete_AT method as a completion handler)

Some "_parent" related features are still broken
XVimArgumentEvaluator now can be used as a simple argument evaluator.
You just use it as a next evaluator and use the it result in onChildComplete handler.