RSpec 3 doesn’t have a nested formatter (it’s documentation).
Improve footer CSS.

- 130px looked too big to me.  The header nav 78px,
  so let’s match that.
- Center-align the text. It looked weird being on the left.
- Add a bit more padding so it looks vertically centered
  in the footer.
Put About before Documentation.

It feels more natural (to me) for it to go first.
Add upgrade article.
Add upgrade link to header.
Merge pull request #25 from rspec/myron-further-changes

A few changes