Support for title and meta description via annotations

I am using this tool to build a website for a project I am working on. Since I am generating a number of html pages from markdown files I thought it'd be nice to being able to specify title and description for the pages so search engines are happier.

I added a couple of lines of code that given a `*.md` file annotated with:

    <!--
    @-title:nice page title
    @-description: google will love this!
    -->

generate the corresponding `title` and `meta` tags in the HTML.

Unit tests are also included.

Feel free to merge if you'd like to have this feature. If not no problem, I'll just keep using my fork.