Fix Interactable#unset's event removal
Improve comment formatting
Improve interaction setting and event binding

Events listeners can be bound to Interactables as the action is enabled
with the Interactable#<action>able methods. eg:
```
interact(el).draggable({
        onstart: function (event) {
            // respond to dragstart event
        },
        onmove: function (event) {
            // respond to dragmove event
        },
        onend: function (event) {
            // respond to dragend event
        }
    });
README: begin with a quick sampe