Added Markdown file for generating documentation

Added `doc/apimd.md` for generating almost identical api with [synbioz/md](https://github.com/synbioz/md). The Markdown file could also be used in the github wiki.

I forked the [synbioz/md](https://github.com/synbioz/md) project and added a feature which allows to use a custom CSS file. My fork can be found here: [X455u/md](https://github.com/X455u/md)
The command to generate the html file with my fork would be `thor md:generate apimd.md -c apidoc.css`

I also changed the CSS a bit to make the following HTML look better
```HTML
<pre>
  <code>
line 1 of code
line 2 of code
line 3 of code
  </code>
</pre>
```