code: function Loop(messenger)
  {
    // Messenger we'll use for clock signals
    this.messenger = messenger || new Messenger();
  
    this.fixedDuration = 8;
    this.started       = false;
  
    // Live stats
    this.currentTime        = 0;
    this.fixedStepsPerFrame = 0;
    this.fixedTimePerFrame  = 0;
    this.renderTimePerFrame = 0;
    this.frameTime          = 0;
  }
docs: Game loop with independent clock events for fixed durations and variable
  durations.
  @param {Messenger} messenger
  @constructor