title: R change title size in legend
body: <p>I use the R base command "legend" to add a legend to a plot and I want the title of this legend to be bigger.
  In the help it says:</p>
  
  <blockquote>
    <p>cex: character expansion factor <em>relative</em> to current ‘par("cex")’. 
    Used for text, and provides the default for ‘pt.cex’ and ‘title.cex’.</p>
  </blockquote>
  
  <p>But trying to change title.cex  doesn't work and throw a <code>unused argument</code> error.</p>
  
  <p>Here an example:</p>
  
  <pre><code>plot(1:10,10:1)
  legend("topright",title="I need that bigger",legend="points",pch=21)
  </code></pre>