title: Tracking Ahoy custom event in Rails model
body: <p>I'm not sure how to use custom event tracking in ahoy. I followed the documentation and added a</p>
  
  <pre><code>ahoy.track "Viewed book", title: "Hot, Flat, and Crowded"
  </code></pre>
  
  <p>in one of my models, but I get</p>
  
  <pre><code>undefined local variable or method `ahoy'
  </code></pre>
  
  <p>Are controllers the only place where I can track ahoy events?</p>