Add a header parser

You are now able to add this kind of headers on the top of 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).

You also have to set a *config.json* property:

    parseHeader: true