Child view controllers

So after reading over the notes on ["Implementing a Container View Controller"](http://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIViewController_Class/Reference/Reference.html) again, I think I've backtracked on the decision to have an explicit `drawerWillAppear` method in the category. I think it does make sense to properly use the view Will/Did dis/appear methods, so this pull takes a stab at doing this.

**NOTE**: I don't want this merged in yet, I'm just putting it up for review and want to get your thoughts.

**TIL** don't manually call view Will/Did dis/appear from the parent view controller.

If we go with this decision, we'll need to bump to 0.1.0.