Add markdown

I have added markdown using [django-pagedown](https://github.com/timmyomahony/django-pagedown) and [django-markdown-deux](https://github.com/trentm/django-markdown-deux).

The choice was either a combination of the two or [django-markdown](https://github.com/klen/django_markdown), but django_markdown uses `markdown` as opposed to `markdown2`. `markdown2` is apparently superior.

There are a few other changes too, but they're pretty minor. Comments welcome :)