Fixed invalid HTML markup in category_index template.
Changed unit-section to class.
Enabled TOC generation for rdiscount.

It uses a different style to the old markdown parser so old links will have to be updated.
Improved article footer.

Now only shows links to next/previous articles. Also, it's less wordy.
Styled tables.
Capitalised <h3> elements.

Essentially, I'm copying A List Apart's style guide. One day, I will decide on a style guide to follow for this site. Today is not that day though.