Expose extendPrototype as factory.extend

[kixxauth]

It would be great if we could treat factory functions like traditional JavaScript constructor functions, but with some sugar. So you could do something like this:

var Mammal = BRIXX.factory();
Mammal.prototype; // {} blank Object

var Cat = Mammal.extend(EventEmitter.prototype, {
    legs: function () { return 4; }
});
Cat.prototype; // Includes Mammal, EventEmitter, and {legs: }

Would require #13