Sets this's status_code to status_code and adds a Location header pointing to
redirect_uri.
Use this from a [class@Server] when you want to redirect the client to another URI.
redirect_uri can be a relative URI, in which case it is interpreted relative to this's
current URI. In particular, if redirect_uri is just a path, it will replace the path *and query* of
this's URI.
| this | |
| status_code |
a 3xx status code |
| redirect_uri |
the URI to redirect this to |