(#1554) Add support for all common compressions (write and read)

- Remove the context.Context interface and export the *context, the iris.Context now points to the pointer\nSupport compression and rate limiting in the FileServer\nBit of code organisation


Former-commit-id: ad1c61bf968059510c6be9e7f2cceec7da70ba17

_examples/response-writer/write-gzip/main.go

@@ -1,24 +0,0 @@
-package main
-
-import "github.com/kataras/iris/v12"
-
-func main() {
-	app := iris.New()
-	// app.Use(iris.Gzip)
-	// func(ctx iris.Context) { ctx.Gzip(true/false)}
-	// OR:
-	app.Get("/", func(ctx iris.Context) {
-		ctx.WriteGzip([]byte("Hello World!"))
-		ctx.Header("X-Custom",
-			"Headers can be set here after WriteGzip as well, because the data are kept before sent to the client when using the context's GzipResponseWriter and ResponseRecorder.")
-	})
-
-	app.Get("/2", func(ctx iris.Context) {
-		// same as the `WriteGzip`.
-		// However GzipResponseWriter gives you more options, like
-		// reset data, disable and more, look its methods.
-		ctx.GzipResponseWriter().WriteString("Hello World!")
-	})
-
-	app.Listen(":8080")
-}