added fix for all bound events responding to all instances

Due to the way the events class was being mixed-in directly onto the prototype, every instance of the Animation class shared the same event handlers. In other words, if you have 50 instances of the `Animation` class in your app, and bind a handler to `frame` on each, calling `animateTo` on a single instance would fire all 50 event handlers. This mixes-in the `Events` class in the `Animation` constructor, giving each instance a separate `handlers` array.

Signed-off-by: Darcy Adams <darcy.adams@wellogic.com>