[2.0-wip] Hero example lacks proper CSS

Created by: maximz

In 2.0-wip, the hero.html example lacks some CSS that is currently included in the master branch.

Compare the following pages: http://twitter.github.com/bootstrap/examples/hero.html - master branch http://markdotto.com/bs2/examples/hero.html - 2.0-wip, without .hero-unit CSS

If the examples are linked to from the docs, just as in v1, this could be an important bug. If I have time tomorrow, I'll fix this and submit a pull request.