Made the archived downloads better readable

overhaul of http://openra.res0l.net/assets/downloads/ with a preview already in place because I experimented with the `.htaccess` file there. See http://httpd.apache.org/docs/current/mod/mod_autoindex.html for the magic used.

![styled-downloads](https://f.cloud.github.com/assets/756669/1751076/becf7a66-65c8-11e3-9bef-c6afb0baf779.png)