Add Fully-Fledged Events to the Date Picker

Hello,

It would be nice if this were able to bind multiple callbacks per event. I added an events subsystem (identical in API to that in use by Backbone, except for the addition of `triggerMethod` from Backbone.Marionette) and modified it slightly to call the event callbacks from the configuration object. This change won't break the API for existing users; it'll just add the ability to use `on`, `off`, `once`, etc. to bind multiple callbacks to each event.

I had written this events subsystem for another project: https://github.com/mcordingley/Appliance The events are fully unit-tested in that project.