Added bubbling events via `return true`

If you return true from an event handler, the
event will bubble up to a parent route. No exception
is thrown if an event was handled, bubbles, and isn't
handled again by a parent route.

This is a next step for Ember.js router work.
See https://github.com/emberjs/ember.js/pull/2522
Merge pull request #15 from machty/bubbling-trigger

Added bubbling events via `return true`