fix(example): return proper 404 for unmatched routes

Relates to #60

examples/example_with_default_router.rs

@@ -2,7 +2,8 @@ extern crate serialize;
 extern crate nickel;
 extern crate http;
 
-use nickel::{ Nickel, Request, Response };
+use http::status::{ NotFound };
+use nickel::{ Nickel, Request, Response, ErrorWithStatusCode, Action, NickelError, IntoMiddleware };
 use std::io::net::ip::Ipv4Addr;
 
 fn main() {
@@ -23,5 +24,13 @@ fn main() {
     // go to http://localhost:6767/foo to see this route in action
     server.get("/foo", foo_handler);
 
+    //middleware to catch all non matched routes
+    fn catch_all (_request: &Request, _response: &mut Response) -> Result<Action, NickelError> {
+        Err(NickelError::new("File Not Found", ErrorWithStatusCode(NotFound)))
+    }
+
+    // middleware is optional and can be registered with `utilize`
+    server.utilize(IntoMiddleware::from_fn(catch_all));
+
     server.listen(Ipv4Addr(127, 0, 0, 1), 6767);
 }