Add advanced example source code (#15)

Hi!
From #14, I think it's difficult to understand advanced example in readme.

So that I wrote a working advanced example.

Thanks.

README.md

@@ -25,9 +25,9 @@ import "github.com/gin-contrib/multitemplate"
 
 ### Simple example
 
-See [example/example.go](example/example.go)
+See [example/simple/example.go](example/simple/example.go)
 
-[embedmd]:# (example/example.go go)
+[embedmd]:# (example/simple/example.go go)
 ```go
 package main
 
@@ -64,11 +64,13 @@ func main() {
 
 [Approximating html/template Inheritance](https://elithrar.github.io/article/approximating-html-template-inheritance/)
 
+See [example/advanced/example.go](example/advanced/example.go)
+
+[embedmd]:# (example/advanced/example.go go)
 ```go
 package main
 
 import (
-	"html/template"
 	"path/filepath"
 
 	"github.com/gin-contrib/multitemplate"
@@ -79,30 +81,36 @@ func main() {
 	router := gin.Default()
 	router.HTMLRender = loadTemplates("./templates")
 	router.GET("/", func(c *gin.Context) {
-		c.HTML(200, "index.tmpl", gin.H{
+		c.HTML(200, "index.html", gin.H{
 			"title": "Welcome!",
 		})
 	})
+	router.GET("/article", func(c *gin.Context) {
+		c.HTML(200, "article.html", gin.H{
+			"title": "Html5 Article Engine",
+		})
+	})
+
 	router.Run(":8080")
 }
 
 func loadTemplates(templatesDir string) multitemplate.Renderer {
 	r := multitemplate.NewRenderer()
 
-	layouts, err := filepath.Glob(templatesDir + "/layouts/*.tmpl")
+	layouts, err := filepath.Glob(templatesDir + "/layouts/*.html")
 	if err != nil {
 		panic(err.Error())
 	}
 
-	includes, err := filepath.Glob(templatesDir + "/includes/*.tmpl")
+	includes, err := filepath.Glob(templatesDir + "/includes/*.html")
 	if err != nil {
 		panic(err.Error())
 	}
 
 	// Generate our templates map from our layouts/ and includes/ directories
-	for _, layout := range layouts {
-		files := append([]string{layout}, includes...)
-		r.Add(filepath.Base(layout), template.Must(template.ParseFiles(files...)))
+	for _, include := range includes {
+		files := append(layouts, include)
+		r.AddFromFiles(filepath.Base(include), files...)
 	}
 	return r
 }

example/advanced/example.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"path/filepath"
+
+	"github.com/gin-contrib/multitemplate"
+	"github.com/gin-gonic/gin"
+)
+
+func main() {
+	router := gin.Default()
+	router.HTMLRender = loadTemplates("./templates")
+	router.GET("/", func(c *gin.Context) {
+		c.HTML(200, "index.html", gin.H{
+			"title": "Welcome!",
+		})
+	})
+	router.GET("/article", func(c *gin.Context) {
+		c.HTML(200, "article.html", gin.H{
+			"title": "Html5 Article Engine",
+		})
+	})
+
+	router.Run(":8080")
+}
+
+func loadTemplates(templatesDir string) multitemplate.Renderer {
+	r := multitemplate.NewRenderer()
+
+	layouts, err := filepath.Glob(templatesDir + "/layouts/*.html")
+	if err != nil {
+		panic(err.Error())
+	}
+
+	includes, err := filepath.Glob(templatesDir + "/includes/*.html")
+	if err != nil {
+		panic(err.Error())
+	}
+
+	// Generate our templates map from our layouts/ and includes/ directories
+	for _, include := range includes {
+		files := append(layouts, include)
+		r.AddFromFiles(filepath.Base(include), files...)
+	}
+	return r
+}

example/advanced/templates/includes/article.html

@@ -0,0 +1 @@
+{{define "content"}}Hi, this is article template{{end}}

example/advanced/templates/includes/index.html

@@ -0,0 +1 @@
+{{define "content"}}Hi, this is index.html{{end}}

example/advanced/templates/layouts/base.html

@@ -0,0 +1,3 @@
+Title: {{ .title }}
+
+index template: {{template "content" .}}