title: Dygraphs display year only date value
body: <p>I am developing a bar graph to display a yearly aggregated value compared to a series of other yearly values.  The values are of total water consumption for a year compared to the previous year and so on.  I can't figure out how to format my date field in my CSV for a single yearly value.  Assuming it must be something like 20130101, how do I customise the x axis labl to just show 2013  2012  2011 etc?</p>
  
  <p><strong>CSV</strong></p>
  
  <pre><code>Date,Litres 
  2012,42047 
  2013,18604.5
  </code></pre>
  
  <p><strong>Code</strong></p>
  
  <pre><code>g4 = new Dygraph(document.getElementById("year"),
                   "192.168.252.30/monitoring/data_water_year.php",
                   {legend: 'always', 
                    title: 'Yearly Water Usage', 
                    xlabel: 'Date', 
                    ylabel: 'Litres', 
                    includeZero: true, 
                    animatedZooms: true, 
                    drawXGrid: false, 
                    plotter: barChartPlotter} 
  );
  </code></pre>