title: How to response for wrong passed parameter in Apiary?
body: <p>I saw the following Action section inside of Apiary blueprint examples. I want to response with HTTP status 404 when the user passes a wrong parameter. for example when the user passes /questions/xyz instead of /questions/1.
  As you can see we defined that the parameter after /questions must be a number but when I passed xyz itstead of a number it answer with a same object.</p>
  
  <pre><code>## Questions [/questions/{question_id}]
  An Questions object has the following attributes:
  
  + question - We can put some description for each attribute here.
  + published_at - An ISO8601 date when the question was published.
  + url (string) 
  + choices - An array of Choice objects.
  
  + Parameters
      + question_id: `1` (number, required) - ID of the Questions in form of an integer
  
  ### View an Questions Detail [GET]
  
  + Response 200 (application/json)
  
              {
                  "question": "Favourite programming language?",
                  "published_at": "2014-11-11T08:40:51.620Z",
                  "url": "/questions/1",
                  "choices": [
                      {   &lt;!-- First Object --&gt;
                          "choice": "Swift",
                          "url": "/questions/1/choices/1",
                          "votes": 2048
                      }
                  ]
              }
  
  + Response 404 (text/plain)
  
      There is no such a message for the passed id. For example if you pass 'xyz' we expect to show this message.
  </code></pre>
  
  <p>Please write me complete code.
  Thanks in advance.</p>