New DirOptions.Cache field for in-memory caching and pre-compression for the fastest possible static file server

Read HISTORY.md it contains a breaking change, second parameter of HandleDir should be iris.Dir(...) instead of just a string

relative to: https://github.com/kataras/iris/issues/1556#issuecomment-661057446


Former-commit-id: 14b48a06fb3b99287dff543932be2937a64233b9

_examples/websocket/basic/server.go

@@ -114,7 +114,7 @@ func main() {
 	})
 
 	// serves the npm browser websocket client usage example.
-	app.HandleDir("/browserify", "./browserify")
+	app.HandleDir("/browserify", iris.Dir("./browserify"))
 
 	app.Listen(":8080")
 }