expose route.next() to allow match continuation

Found myself wanting to use the routes module's `match.next()` method with this module.
I'm not sure if this is the best way to expose it, but it works with usage like this:

```
router.addRoute('*', function (req, res, opts) {
  // do something like check auth
  var match = opts.next();
  if (match) match.fn(req, res, match);
});
```