Add aliases for some functions

[Hebo]

This mirrors the Backbonejs events API and to a lesser extent the
Nodejs events API.

• on() = addListener()
• off() = removeListener()
• trigger() = emitEvent()

We use use EventEmitter in more places than Backbone, so it's nice to be able to use the same API between objects that mixin Backbone.Events and those that mixin EventEmitter.

[Hebo]

Looking over at the closed issues, it seems a similar alias was added in #24, but removed in a rewrite (a13f34e).

[Olical]

Yep, they were there at one point but I left them out when I cleaned the whole thing up. I have to admit that addListener is a little long winded. I don't think it's such a bad thing to add them back in. Especially if it makes it a bit easier for everyone to type.

I will merge this in very soon and add each method to the documentation specifying that it's an alias. Thank you!