Add a header parser

You are now able to add this kind of headers to your md files:

```
title: This is the real title
author: John Doe <john.doe@datalove.com>
date: 2014-06-25
keywords: mdwiki, wiki, markdown
```

It will be dynamically added to the *meta tags* of your page.
Plus `document.title` will be set to the defined title, or defaults to
the first header (page first level 1 title).