Redirect to another route

Hey, nice library!

I have been stuck finding an answer.

What I Want:
```php
$router->get('/([a-z0-9_-]+)', function($slug) {
// Code to find the id
$router->callRoute(...); // Some way to call the other route, giving the id as parameter
});

$router->get('/(\d+)', function($id) {
// Code
});
```

What I did so far:
```php
function perId($id) {
// Code
}

$router->get('/([a-z0-9_-]+)', function($slug) {
// Code to find the $id
perId($id);
});

$router->get('/(\d+)', function($id) {
perId($id);
});
```

I don't know if I can accomplish the same with the `before()` function
Please give me your opinion

Start by reviewing the router's route-dispatch behavior and the documented before() hook. Determine whether the requested route-to-route handoff is supported or needs a defined API, including how parameters should be passed. Done means the behavior and its expected usage are clearly specified and verified.

Written by the indexing model from the issue text.