add layouts and inherits

this features only for nodejs in backend. Before use include, you must set the templates dir. You can use the doT.set method to do this, example:

doT.set('dir', '/opt/templete');

then, in the templates, you can use include like this:

// the base.html
<html>
     <head>
           <title>{{#def.title}}</title>
     </head>

     <body>
          {{#def.body}}
     </body>
</html>

// the sub page
{{>base.html}}
{{##def.title:
document title
#}}

{{##def.body:
     <div>the body</div>
#}}