Give a more sensible error message for unhandled routes.

Also redirect any request URLs consisting of double slashes.

src/index.js

@@ -89,6 +89,14 @@ router.get("/", () => {
     return new Response(null, { headers: { "Location": "https://artifactdb.github.io/gypsum-worker" }, status: 301 })
 })
 
+router.all('*', request => { 
+    const u = request.url;
+    if (u.indexOf("//") != -1) {
+        return new Response(null, { headers: { "Location": u.replace(/([^:])(\/\/+)/g, "$1/") }, status: 301 })
+    }
+    return http.errorResponse("no such endpoint", 404);
+})
+
 export default {
 
 fetch(request, env, context) {