add Context.ResponseWriter.IsHijacked to report whether the underline conn is already hijacked and a lot of cleanup and minor ws stress test example improvements

Former-commit-id: 444d4f0718d5c6d7544834c5e44dafb872980238

doc.go

@@ -1471,7 +1471,7 @@ Example Server Code:
         // see the inline javascript code i the websockets.html, this endpoint is used to connect to the server.
         app.Get("/echo", ws.Handler())
 
-        // serve the javascript built'n client-side library,
+        // serve the javascript builtin client-side library,
         // see websockets.html script tags, this path is used.
         app.Any("/iris-ws.js", func(ctx iris.Context) {
             ctx.Write(websocket.ClientSource)
@@ -1554,7 +1554,7 @@ Example Code:
 
     func main() {
         app := iris.New()
-        // Optionally, add two built'n handlers
+        // Optionally, add two builtin handlers
         // that can recover from any http-relative panics
         // and log the requests to the terminal.
         app.Use(recover.New())