title: how to set the domain and scale on an axis on a nvd3.js multiBarChart
body: <p>In d3.js you can set an x axis to use <code>d3.time.scale()</code> then set <code>x.domain([start_date, end_date])</code> and it will 'fill in' any missing dates that aren't in the data with 0 values. I want to do the same with a nvd3.js <code>mulitBarChart</code>.</p>
  
  <p>This code (can be pasted directly into <a href="http://nvd3.org/livecode/#codemirrorNav">http://nvd3.org/livecode/#codemirrorNav</a>) shows a bar chart of totals by year, there are missing values for 2002 &amp; 2003. I want to set the scale to be <code>d3.time.scale()</code> and then the domain to the first and last years of the dataset so the missing years are automatically added with 0 values. How do I do that?</p>
  
  <pre><code>nv.addGraph(function() {
      var chart = nv.models.multiBarChart();
  
      chart.xAxis
          .tickFormat(function(d){ return d3.time.format('%y')(new Date(d)); });
  
      chart.yAxis
          .tickFormat(d3.format(',f'));
  
      chart.reduceXTicks(false);
      chart.showControls(false);
  
      var data = [{
        'key': 'GB by year',
        'values': [
          {x: new Date().setFullYear('2001'), y: 0.12},
          {x: new Date().setFullYear('2004'), y: 0.03},
          {x: new Date().setFullYear('2005'), y: 0.53},
          {x: new Date().setFullYear('2006'), y: 0.43},
          {x: new Date().setFullYear('2007'), y: 5.5},
          {x: new Date().setFullYear('2008'), y: 9.9},
          {x: new Date().setFullYear('2009'), y: 26.85},
          {x: new Date().setFullYear('2010'), y: 0.03},
          {x: new Date().setFullYear('2011'), y: 0.12}
        ]
      }];        
  
      d3.select('#chart svg')
          .datum(data)
        .transition().duration(500).call(chart);
  
      nv.utils.windowResize(chart.update);
  
      return chart;
  });
  </code></pre>