title: How to add a method to the versions model of Paper_trail?
body: <p>I want to create the following method for paper_trail versions:</p>
  
  <pre><code>def user
    User.find self.whodunnit.to_i
  end
  </code></pre>
  
  <p>So that I can access a version's user naturally in my app as if it has a <code>belongs_to</code> relation.</p>
  
  <p><strong>Where should I put this function (folder and file name) in order to override / add it to paper_trail's version model?</strong></p>