title: Kraken JS middleware and exceptions
body: <p>I'm experimenting with KrakenJS, trying to build an basic API to understand things.</p>
  
  <p>One thing I'm unsure of is the middleware, specifically the 404/500 error handling.</p>
  
  <pre><code>"fileNotFound": {
      "enabled": true,
      "priority": 130,
      "module": {
              "name":"path:./lib/exceptions/404"
      }
  }
  </code></pre>
  
  <p>This catches any 404 errros, and then I handle that myself in my own configuration. However, why is this <code>fileNotFound</code> thrown? Where is <code>serverError</code> thrown for 500 errors?</p>
  
  <p>I would like to define my own files for other exceptions like a 403, however how would I get this to trigger a middleware?</p>