title: Adding thousands separator for custom formatted highcharts tooltip
body: <p>I am using highcharts to in my app and want to add tooltip with thousand separator like I did it in data labels. I used custom formatting for tooltip, so what should I change to achieve this</p>
  
  <p>tooltip options in highcharts</p>
  
  <pre><code>tooltip: {
                  formatter: function () {
                      return (this.x + ':' + this.y);
                  },
                  shared: true,
                  useHTML: true
              },
  </code></pre>
  
  <p><a href="http://jsfiddle.net/shahinul87/s81cnw79/" rel="noreferrer">JS FIDDLE</a></p>