Some modifications to the about page.
Add rule to add space between H1 and aside.

This combination is used on the tag list view to advertise the Atom
feed.
Improve tag list view.

- Change the title to "Articles tagged as XXX".
- Add quotes around the tag name in the link to the Atom feed.
- Remove unneeded 'if' in the template.
Restructure the SASS files.

Inspired by http://css-tricks.com/sass-style-guide/