do note explicitly require Controller#call method

I found it slightly odd that I needed to always write a `.call` method in my controllers when that method was empty.  So instead I decided to [check for the existence of the super method] (http://devblog.avdi.org/2010/09/24/checking-the-existence-of-a-super-method-in-ruby/) in the parent class first.

Why no tests?  Well, originally I did write a test, but given that minitest does not have a `wont_raise` function, and given that tests really shouldn't be testing for *not* raising things (as it is implicit), I found tests not to be necessary.