Make routing feature class public

- Made routing feature class public, to lower boilerplate code in client
code tests.

Addresses #333

src/Microsoft.AspNetCore.Routing/RouterMiddleware.cs

@@ -48,10 +48,5 @@ public async Task Invoke(HttpContext httpContext)
                 await context.Handler(context.HttpContext);
             }
         }
-
-        private class RoutingFeature : IRoutingFeature
-        {
-            public RouteData RouteData { get; set; }
-        }
     }
 }

src/Microsoft.AspNetCore.Routing/RoutingFeature.cs

@@ -0,0 +1,10 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.AspNetCore.Routing
+{
+    public class RoutingFeature : IRoutingFeature
+    {
+        public RouteData RouteData { get; set; }
+    }
+}