code: function render_with_layout(template, locals, cb) {
      render_file(locals, function(err, str) {
        if (err) {
          return cb(err);
        }
  
        locals.body = str;
  
        var res = template(locals, handlebarsOpts);
        self.async.done(function(values) {
          Object.keys(values).forEach(function(id) {
            res = res.replace(id, values[id]);
          });
  
          cb(null, res);
        });
      });
    }
docs: render with a layout