Extract InvokeRoute method to allow overriding (#176)

* Extract InvokeRoute method to allow overridingit.

* Remove commented code.

Author: torbacz

nanoFramework.WebServer/WebServer.cs

@@ -580,7 +580,7 @@ private void StartListener()
 
                         if (isAuthOk)
                         {
-                            route.Callback.Invoke(null, new object[] { new WebServerEventArgs(context) });
+                            InvokeRoute(route, context);
                         }
                         else
                         {
@@ -638,6 +638,16 @@ private void StartListener()
             }
         }
 
+        /// <summary>
+        /// Method which invokes route. Can be overriden to inject custom logic.
+        /// </summary>
+        /// <param name="route">Current rounte to invoke. Resolved based on parameters.</param>
+        /// <param name="context">Context of current request.</param>
+        protected virtual void InvokeRoute(CallbackRoutes route, HttpListenerContext context)
+        {
+            route.Callback.Invoke(null, new object[] { new WebServerEventArgs(context) });
+        }
+
         private string GetApiKeyFromHeaders(WebHeaderCollection headers)
         {
             var sec = headers.GetValues("ApiKey");