code: function update(req, res, next) {
    var body = req.body;
  
    db.posts.update(req.params.post, body, function(err, post) {
      if(err) { return next(err); }
  
      res.json(201, post);
      signals.emit('post:update', post);
    });
  }
docs: URL: /posts/:post
  
  Method: PUT
  
  Events:
  
  * `post:update` (post)
  
  Status codes:
  
  * `201` if post was created successfully
  * `409` if a post with the same `slug` already exists