feat(uri): add is_absolute method to Uri

This allows servers to check if an incoming URI is in absolute form.
Especially useful for proxies to determine if the request was meant to
be proxied or aimed directly at the proxy server.

src/uri.rs

@@ -190,6 +190,14 @@ impl Uri {
         })
     }
 
+    /// Returns whether this URI is in `absolute-form`.
+    ///
+    /// An example of absolute form is `https://hyper.rs`.
+    #[inline]
+    pub fn is_absolute(&self) -> bool {
+        self.scheme_end.is_some()
+    }
+
     #[cfg(test)]
     fn fragment(&self) -> Option<&str> {
         self.fragment_start.map(|start| {