Add document or example for the new event module

[igaryhe]

I've noticed that there is a significant API change between 0.2.1 and the current master branch in the event module. While I was quite familiar with the original event channel concept used in 0.2.1, I'm quite confused by the current event module. I'm not sure how to use it. It would be beneficial if you could provide some documents or examples to demonstrate the usage.