title: ggplot2: Put multi-variable facet_wrap labels on one line
body: <p>I am using facet_wrap to split my scatter plot as</p>
  
  <pre><code>facet_wrap(x~y+z)
  </code></pre>
  
  <p>This generates 22 plots in my case as desired. However, label for each of those 22 plots is displayed in 3 rows (x, y and z) which unnecessarily consumes the space in the window and squishes the plots into a small area. I would rather want my plots to be bigger in size. Since variables y and z are short, I would like to display them in same row instead of two. </p>
  
  <p>I looked into the labeller options but none of them seem to do what I would want. I would appreciate any suggestions here.</p>