feature request: yaml vars in beginning of the layout

Hi!
I have an idea use [front-matter](https://www.npmjs.com/package/front-matter) package
PR Welcome?
```
---
title: Just hack'n
description: Nothing to see here
---
<html>
    <head>
        <title>{{ title }}</title>
        <meta name="description" content="{{ description }}" >
    </head>
    ....
</html>
```