Event listeners for when objects are added, updated, or deleted
First of all, thank you for this library.

I'm just wondering if I can attach an event listener for when an object is added, updated, or deleted from the canvas? I'm using this library to create a collaborative whiteboard app, so I'll need to listen for those events.

I created a fork here: https://github.com/anchetaWern/react-sketch But I don't really know how to compile so I couldn't get the changes I've made to work.