title: Enable fullscreen on youtube iframe video
body: <p>I create iframe youtube vidéo with this code:</p>
  
  <pre><code>var tag = document.createElement('script');
  tag.src = "//www.youtube.com/iframe_api";
  var firstScriptTag = document.getElementsByTagName('script')[0];
  firstScriptTag.parentNode.insertBefore(tag, firstScriptTag);
  
  // ...
  
  _yt_player = new YT.Player("#myobjectytiframe", {
    height  : 640,
    width   : 480,
    videoId : video_id,
    events  : {
      'onReady': function(){
          _yt_player.playVideo();
          // ENABLE FULLSCREEN
      },
      'onStateChange': function(){},
      'onError': function(){}
    }
  });
  </code></pre>
  
  <p>I would like to enable fullscreen in <code>onReady</code> callback, how to do that ?</p>