title: High Charts for an area-spline chart with area fill on only one data set in series
body: <p>I would like to make an area-spline chart very similar to the one that is demo'd on the High Charts website(<a href="http://www.highcharts.com/demo/areaspline" rel="nofollow">http://www.highcharts.com/demo/areaspline</a>). The main difference that I need to implement would be that I only need one of the data sets to have the area fill, and the other data sets be regular splines. By looking at the documentation, it appears that the options that relate to the area fill are applied to all data sets - I don't see a way to set options for individual datasets.</p>
  
  <p>Is it possible to build an area-spline like this? If so, what am I missing in the docs that would let me do so?</p>