title: Toggle class on click directive?
body: <p>Is there a way to add and remove a class using a directive when an element is clicked?</p>
  
  <p>I want to avoid putting the element into a template and just use a directive.</p>
  
  <p>So something like:</p>
  
  <pre><code>&lt;div v-toggle-class&gt;&lt;/div&gt;
  </code></pre>
  
  <p>Then this would toggle a predefined class like <code>.active</code></p>