I really like the code, I think it's very well written!

A couple small suggestions and thoughts:

Add a couple lines so that all methods return this; to allow for chaining, especially helpful when using it as a mixin.

Rename bind/unbind method names since they have completely different meanings/uses in ES5:

https://developer.mozilla.org/en/JavaScript/Reference/Global...

P.S. If you're down with those changes I'll gladly fork, update and send a pull req, although not sure what you'd want to rename the api too.