code: function createEventTracker (emitter) {
    const events = []
    return {
      on (event, fn) {
        events.push([ event, fn ])
        return emitter.on(event, fn)
      },
      remove () {
        events.forEach(([ event, fn ]) => {
          emitter.off(event, fn)
        })
      }
    }
  }
docs: Create a wrapper around an event emitter with a `remove` method to remove
  all events that were added using the wrapped emitter.