Add a 'ParseTemplate' method on view engines to manually parse and add a template from a text

examples at: https://github.com/kataras/iris/tree/master/_examples/view/parse-template

relative to: https://github.com/kataras/iris/issues/1617

_examples/view/parse-template/handlebars/main.go

@@ -0,0 +1,24 @@
+package main
+
+import "github.com/kataras/iris/v12"
+
+func main() {
+	e := iris.Handlebars(nil, ".html") // You can still use a file system though.
+	e.ParseTemplate("program.html", `<h1>{{greet Name}}</h1>`, iris.Map{
+		"greet": func(name string) string {
+			return "Hello, " + name + "!"
+		},
+	})
+
+	app := iris.New()
+	app.RegisterView(e)
+	app.Get("/", index)
+
+	app.Listen(":8080")
+}
+
+func index(ctx iris.Context) {
+	ctx.View("program.html", iris.Map{
+		"Name": "Gerasimos",
+	})
+}