title: variable vertex font size in igraph
body: <p>Is it possible have vertex labels of variable font sizes.
  labelling certain nodes with a bigger font size than others </p>
  
  <pre><code>g1 &lt;- erdos.renyi.game(20, 2/20)
  V(g1)$name&lt;-letters[1:vcount(g1)]
  plot(g1,vertex.label=V(g1)$name)
  </code></pre>
  
  <p>Understand there is a vertex.label.cex option in igraph.plot but it is global. </p>