openlayers/ol3 — pull request #1297 by tschaub (2013-12-05 19:30:15+00:00)
Title: Create ol.Observable

Instances of `ol.Object` get the convenient `on`, `once`, and `un` methods for registering listeners. If moved these methods to a new `ol.Observable`, other components could extend this without having to be `ol.Object`s as well.