we computed a deltaScore (is a property in cardMatchingGame) for use in the controller’s label.

Homework: Implement the history MVC and everything that goes along with it.
	Notes: we plan to cache the history in a public property in the model. it will be cached (like the verb) in the event label text generation method in the model.
		we also put an if statement on line 109 of CardMatchingGame.m which is where a match must have just happened.