restucture content to use dir as category

Thnx to /u/AlZheim3r on reddit for pointing out that
pelican supports using the directory structure to determine
blog post categories. It seems to me that this is a more sane way
to organize posts.

https://www.reddit.com/r/LinuxActionShow/comments/2ncnzg/dump_wordpress_for_static_blog_generator/cmciruq