title: highchart position label on xAxis value
body: <p>Using highchart, is there a way to add labels according to particular x / y Axis values ?</p>
  
  <p>Using the <a href="http://api.highcharts.com/highcharts#labels" rel="nofollow">highchart's labels</a>, I'm able to write text at a given position in pixels, but I need to give a value from an axis as position.</p>
  
  <p>For example, in <a href="http://jsfiddle.net/DdkDW/4/" rel="nofollow">this jsFiddle</a> I would like to set the label position on 'june', like the plot line. </p>
  
  <p>how can I do this?</p>
  
  <pre><code>    labels: { 
             items : [{ 
                 html : 'Summer starts here !' ,
                 style : { 
                     left: '10px', 
                     //I need to set the left position as an xValue : the timestamp for the summer start.
                     top: '100px'
                 }
             }] 
      }
  </code></pre>