Commit WIP on router

There are a few different changes in here that probably need to be picked
apart. I'm sure much of this is wrong.

* Fix missing `dyn` that compiler complained about in router.rs

* Make UseRoute store a `Rc<RouterService>` rather than a string so we can get
information out of the router like current location.

* Implement `UseRoute`'s nth_segment and last_segment methods. I changed the
return type to a String because of the above.

* Remove some unused imports in platform/mod.rs and service.rs

* Implement the `use_route` fn. It panics if called outside a Router { } (I
think). I think that makes sense.

* Add a `current_location` method to `RouterService` that returns the current
location. I needed this both for the `UseRoute` implementation and _also_ so I
could get at this in my webapp code. I think having some way to get this will
be useful for others, whether or not this exact API is used. In my case, I
want to compare the current path to the `to` path of a `Link` so I can use a
different class for that `Link` if it is the currently active page.

packages/router/src/hooks/use_route.rs

@@ -1,7 +1,11 @@
 use dioxus_core::ScopeState;
+use gloo::history::Location;
+use std::rc::Rc;
+
+use crate::RouterService;
 
 pub struct UseRoute<'a> {
-    cur_route: String,
+    router: Rc<RouterService>,
     cx: &'a ScopeState,
 }
 
@@ -11,20 +15,44 @@ impl<'a> UseRoute<'a> {
         todo!()
     }
 
-    pub fn nth_segment(&self, n: usize) -> Option<&str> {
-        todo!()
+    pub fn nth_segment(&self, n: usize) -> Option<String> {
+        let mut segments = self.path_segments();
+        let len = segments.len();
+        if len - 1 < n {
+            return None;
+        }
+        Some(segments.remove(n))
     }
 
-    pub fn last_segment(&self) -> Option<&'a str> {
-        todo!()
+    pub fn last_segment(&self) -> Option<String> {
+        let mut segments = self.path_segments();
+        let len = segments.len();
+        if len == 0 {
+            return None;
+        }
+        Some(segments.remove(len - 1))
     }
 
     /// Parse the segments of the URL, using named parameters (defined in your router)
     pub fn segment<T>(&self, name: &str) -> Option<&T> {
         todo!()
     }
+
+    pub fn current_location(&self) -> Location {
+        self.router.current_location()
+    }
+
+    fn path_segments(&self) -> Vec<String> {
+        let location = self.router.current_location();
+        let stripped = &location.path()[1..];
+        stripped.split('/').map(str::to_string).collect::<Vec<_>>()
+    }
 }
 
 pub fn use_route<'a>(cx: &'a ScopeState) -> UseRoute<'a> {
-    todo!()
+    let router = cx
+        .consume_context::<RouterService>()
+        .expect("Cannot call use_route outside the scope of a Router component")
+        .clone();
+    UseRoute { router, cx }
 }