title: Invert y-axis in barplot
body: <p>When I do this:</p>
  
  <pre><code>barplot(c(1,2,3),ylim=c(4,1))
  </code></pre>
  
  <p>I expect the first bar in the barplot to go from 4 to 1. The second bar should go from 4 to 2 and so on. But that's not what I get. How can I achieve this?</p>