title: Set Additional Data to highcharts series
body: <p>is there any way to pass some additional data to the series object that will use to show in the chart 'tooltip'?</p>
  
  <p>for example  </p>
  
  <pre><code> tooltip: {
       formatter: function() {
                 return '&lt;b&gt;'+ this.series.name +'&lt;/b&gt;&lt;br/&gt;'+
             Highcharts.dateFormat('%b %e', this.x) +': '+ this.y;
       }
  </code></pre>
  
  <p>here we can only use series.name , this.x &amp; this.y to the series. lets say i need to pass another dynamic value alone with the data set and can access via series object. is this possible? </p>
  
  <p>Thank you all in advance.</p>