title: color segments in radarchart
body: <p>I recently discovered the rcharts package an was able to make a chart. 
  Now I would like to color segments in the radar chart. Any ideas?
  Below is a simplified example to work on:</p>
  
  <pre><code>library(rCharts)
  #create dummy dataframe with number ranging from 0 to 1
  df&lt;-data.frame(id=c("a","b","c","d","e"),val1=runif(5,0,1),val2=runif(5,0,1))
  #muliply number by 100 to get percentage
  df[,-1]&lt;-df[,-1]*100
  
  plot &lt;- Highcharts$new()
  plot$chart(polar = TRUE, type = "line",height=500)
  plot$xAxis(categories=df$id, tickmarkPlacement= 'on', lineWidth= 0)
  plot$yAxis(gridLineInterpolation= 'circle', lineWidth= 0, min= 0,max=100,endOnTick=T,tickInterval=10)
  plot$series(data = df[,"val1"],name = "Series 1", pointPlacement="on")
  plot$series(data = df[,"val2"],name = "Series 2", pointPlacement="on")
  plot
  </code></pre>
  
  <p>Resulting in a plot like this:</p>
  
  <p><img src="https://i.stack.imgur.com/IUTfB.jpg" alt="rachrt"></p>
  
  <p>Now I would like to produce this plot:</p>
  
  <p><img src="https://i.stack.imgur.com/mERvD.png" alt="enter image description here"></p>