title: Mixing styles in Vis.js charts
body: <p>I am trying to create a 2D chart with a mix of bar graphs and line graphs using Vis.js timeline (graph2d).</p>
  <p>I have tried using groups to define the different graphs, which works fine as long as the groups are of the same style.</p>
  <p>Specifying the style of each group by adding the style as an option to each group, as shown below, does nothing.</p>
  <pre><code>var groups = new vis.DataSet();
  groups.add({ id: 0, content: 'group0', options:{style:'bar'}});
  groups.add({ id: 1, content: 'group1', options:{style:'line'}});
  </code></pre>
  <p>The style of all groups in the chart is the same and seems to be only defined by the <code>style</code> attribute specified directly in the options passed to the graph2d constructor.</p>
  <p>I have searched around (Google, SO, the Vis.js Github page, etc.), but it does not seem like an issue anyone else has - or no one is using mixed charts, which I doubt).</p>
  <p>Is this not possible with Vis.js (old documentation and examples suggests that it has been possible)?</p>