reorganization of _examples and add some new examples such as iris+groupcache+mysql+docker

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/http-server/graceful-shutdown/custom-notifier/main.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	stdContext "context"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"github.com/kataras/iris/v12"
+)
+
+func main() {
+	app := iris.New()
+
+	app.Get("/", func(ctx iris.Context) {
+		ctx.HTML("<h1>hi, I just exist in order to see if the server is closed</h1>")
+	})
+
+	go func() {
+		ch := make(chan os.Signal, 1)
+		signal.Notify(ch,
+			// kill -SIGINT XXXX or Ctrl+c
+			os.Interrupt,
+			syscall.SIGINT, // register that too, it should be ok
+			// os.Kill  is equivalent with the syscall.Kill
+			os.Kill,
+			syscall.SIGKILL, // register that too, it should be ok
+			// kill -SIGTERM XXXX
+			syscall.SIGTERM,
+		)
+		select {
+		case <-ch:
+			println("shutdown...")
+
+			timeout := 10 * time.Second
+			ctx, cancel := stdContext.WithTimeout(stdContext.Background(), timeout)
+			defer cancel()
+			app.Shutdown(ctx)
+		}
+	}()
+
+	// Start the server and disable the default interrupt handler in order to
+	// handle it clear and simple by our own, without any issues.
+	app.Listen(":8080", iris.WithoutInterruptHandler)
+}