an attempt at differentiating event handlers via an optional namespace

I've made an attempt at solving the problem raised in issue #90. This approach allows the user to specify an optional 'namespace' parameter to the on & off methods which allows for multiple independent handlers to be registered for each event.

I wanted to get your feedback before pursuing this approach further. There is at least one immediate issue in that the 'load' event is fired without a 'currentElement' being specified but I didn't want to spend time addressing that if you don't agree with the overall direction.

Let me know your thoughts.