docs: function archive(req, res, next) {
    var years;
  
    db.posts.archive(function(err, posts) {
      if(err) { return next(err); }
  
      years = _.groupBy(posts, function(post) {
        return post.created_at.getFullYear();
      });
  
      res.format({
        'text/html': function() {
          res.render('posts/archive', {years: years});
        },
        'application/json': function() {
          res.json(years);
        }
      });
    });
  }