Full support of the http.FileSystem on all view engines as requested at #1575

Also, the HandleDir accepts both string and http.FileSystem (interface{}) (like the view's fs)

_examples/view/template_pug_0/templates/index.pug

@@ -1,25 +1,20 @@
-mixin withGo
-  | Generating Go html/template output.
-
 doctype html
 html(lang="en")
-  head
-    title= .pageTitle
-    script(type='text/javascript').
-      if (foo) {
-         bar(1 + 5)
-      }
-  body
-    h1 Jade - template engine
-    #container.col
-      if .youAreUsingJade
-        p {{ greet "iris user" }} <!-- execute template funcs -->
-        p You are amazing!
-      else
-        p Get on it!
-      p.
-        Jade is #[a(terse)] and simple
-        templating language with a
-        #[strong focus] on performance
-        and powerful features.
-      + withGo
+	head
+		meta(charset="utf-8")
+		title Title
+	body
+		p ads
+		ul
+			li The name is {{.Name}}.
+			li The age is {{.Age}}.
+
+		each _,_ in .Emails
+			div An email is {{.}}
+
+		| {{ with .Jobs }}
+			each _,_ in .
+				div
+				 An employer is {{.Employer}}
+				 and the role is {{.Role}}
+		| {{ end }}