add rewritten router book and fix features code

docs/router/src/features/failures/named.md

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+# Named Navigation Failure
+
+When using [named navigation](../navigation/name.md), the router runs into a
+problem under these circumstances:
+1. The name we try to navigate to is not contained within our routes.
+2. The route we navigate to requires a parameter that we don't provide when
+   triggering the navigation.
+
+> Users cannot directly interact with named navigation. If a named navigation
+> failure occurs, your app (or the router) has a bug.
+
+The router reacts to this problem differently, depending on our apps build kind.
+
+## Debug
+When running a debug build, the router will `panic` whenever it encounters an
+invalid navigation. This ensures that we notice these problems when we are
+testing our application.
+
+## Release
+When running a release build, the router can't just `panic`, as that would be a
+horrible user experience. Instead, it changes shows some fallback content.
+
+> You can detect if the router is in the named navigation failure handling state
+> by [checking](../navigation/name.md#check-if-a-name-is-present) if the
+> [`FailureNamedNavigation`] name is present.
+
+The default fallback explains to the user that an error occurred and asks them
+to report the bug to the app developer.
+
+You can override it by setting the `failure_named_navigation` value of the
+[`RouterConfiguration`].
+
+```rust,no_run
+# // Hidden lines (like this one) make the documentation tests work.
+# extern crate dioxus;
+# use dioxus::prelude::*;
+# extern crate dioxus_router;
+# use dioxus_router::prelude::*;
+fn NamedNavigationFallback(cx: Scope) -> Element {
+    cx.render(rsx! {
+        h1 { "Named navigation failure!" }
+    })
+}
+
+fn App(cx: Scope) -> Element {
+    use_router(
+        &cx,
+        &|| RouterConfiguration {
+            failure_named_navigation: comp(NamedNavigationFallback),
+            ..Default::default()
+        },
+        &|| Segment::empty()
+    );
+
+    cx.render(rsx! {
+        Outlet { }
+    })
+}
+```
+
+[`FailureNamedNavigation`]: https://docs.rs/dioxus-router-core/latest/dioxus_router_core/prelude/struct.FailureNamedNavigation.html
+[`RouterConfiguration`]: https://docs.rs/dioxus-router/latest/dioxus_router/hooks/struct.RouterConfiguration.html