Expose a way to start/stop listening observable reads outside of a function

[BigAB]

To solve the problem where, the reads that need to be observed are not encapsulated in a function calls.

This will probably require changing observation to allow not providing a function as the first argument:

var observation = new Observation(null, null, function(newVal, oldVal, batchNum){
    console.log("callback", newVal, oldVal, batchNum);
    this.reRender()
})

So that we can observe the operation asynchronously and update in some callback

  componentWillUpdate() {
    observation.pushToStack()
  }
  componentDidUpdate() {
    observation.popFromStack()
  }

[BigAB]

If we expose the stateful parts of can-observation, observationStack and the remaining counter object, we could subclass and have this kind of modification in ur code without making changes to the core can-observation