title: Rivets Formatter not available
body: <p>I am having trouble with getting a formatter to work properly in rivets. </p>
  
  <pre><code>&lt;span class='person-gender' rv-text='person:gender | gender'&gt;&lt;/span&gt;
  </code></pre>
  
  <p>When I check the formatters declared on rivets with rivets.formatters, I see my formatter, but it is never applied.</p>
  
  <p>Within Binding.prototype.formattedValue:398, I see:</p>
  
  <pre><code>else if (formatter instanceof Function) {
      value = formatter.apply(...)
  }
  </code></pre>
  
  <p>But my formatter is not an instance of Function despite it being defined like so:</p>
  
  <pre><code>rivets.formatters.gender = function (value) {
      return value.charAt(0)
  }
  </code></pre>
  
  <p>I am not sure why this formatter is not being applied. I declared it in the same place where I attached my backbone adapter. Any thoughts?</p>