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

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/recover/main.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"github.com/kataras/iris/v12"
+
+	"github.com/kataras/iris/v12/middleware/recover"
+)
+
+func main() {
+	app := iris.New()
+	app.Use(recover.New())
+
+	i := 0
+	// let's simulate a panic every next request
+	app.Get("/", func(ctx iris.Context) {
+		i++
+		if i%2 == 0 {
+			panic("a panic here")
+		}
+		ctx.Writef("Hello, refresh one time more to get panic!")
+	})
+
+	// http://localhost:8080, refresh it 5-6 times.
+	app.Listen(":8080")
+}
+
+// Note:
+// app := iris.Default() instead of iris.New() makes use of the recovery middleware automatically.