code: function(req, res, next) {
          var parsed = require("url").parse(req.url);
          if (parsed.pathname.match(/\.less$/)) {
              return less(parsed.pathname).then(function(o) {
                  res.setHeader("Content-Type", "text/css");
                  res.end(o.css);
              });
          }
          next();
      }
docs: Catch all requests, if any are for .less files, recompile on the fly and
  send back a CSS response