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

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/response-writer/cache/simple/main.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"time"
+
+	"github.com/kataras/iris/v12"
+
+	"github.com/kataras/iris/v12/cache"
+)
+
+var markdownContents = []byte(`## Hello Markdown
+
+This is a sample of Markdown contents
+
+ 
+
+Features
+--------
+
+All features of Sundown are supported, including:
+
+*   **Compatibility**. The Markdown v1.0.3 test suite passes with
+    the --tidy option.  Without --tidy, the differences are
+    mostly in whitespace and entity escaping, where blackfriday is
+    more consistent and cleaner.
+
+*   **Common extensions**, including table support, fenced code
+    blocks, autolinks, strikethroughs, non-strict emphasis, etc.
+
+*   **Safety**. Blackfriday is paranoid when parsing, making it safe
+    to feed untrusted user input without fear of bad things
+    happening. The test suite stress tests this and there are no
+    known inputs that make it crash.  If you find one, please let me
+    know and send me the input that does it.
+
+    NOTE: "safety" in this context means *runtime safety only*. In order to
+    protect yourself against JavaScript injection in untrusted content, see
+    [this example](https://github.com/russross/blackfriday#sanitize-untrusted-content).
+
+*   **Fast processing**. It is fast enough to render on-demand in
+    most web applications without having to cache the output.
+
+*   **Routine safety**. You can run multiple parsers in different
+    goroutines without ill effect. There is no dependence on global
+    shared state.
+
+*   **Minimal dependencies**. Blackfriday only depends on standard
+    library packages in Go. The source code is pretty
+    self-contained, so it is easy to add to any project, including
+    Google App Engine projects.
+
+*   **Standards compliant**. Output successfully validates using the
+    W3C validation tool for HTML 4.01 and XHTML 1.0 Transitional.
+
+	[this is a link](https://github.com/kataras/iris) `)
+
+// Cache should not be used on handlers that contain dynamic data.
+// Cache is a good and a must-feature on static content, i.e "about page" or for a whole blog site.
+func main() {
+	app := iris.New()
+	app.Logger().SetLevel("debug")
+	app.Get("/", cache.Handler(10*time.Second), writeMarkdown)
+	// saves its content on the first request and serves it instead of re-calculating the content.
+	// After 10 seconds it will be cleared and reset.
+
+	app.Listen(":8080")
+}
+
+func writeMarkdown(ctx iris.Context) {
+	// tap multiple times the browser's refresh button and you will
+	// see this println only once every 10 seconds.
+	println("Handler executed. Content refreshed.")
+
+	ctx.Markdown(markdownContents)
+}
+
+/* Note that `HandleDir` does use the browser's disk caching by-default
+therefore, register the cache handler AFTER any HandleDir calls,
+for a faster solution that server doesn't need to keep track of the response
+navigate to https://github.com/kataras/iris/blob/master/_examples/cache/client-side/main.go */