Fix tag styles; add tag-0, de-duplicate tag-2.

There was no style for tag-0. There were two definitions for tag-2.
Merge branch 'tags' of https://github.com/gremmie/pelican-bootstrap3 into gremmie-tags

* 'tags' of https://github.com/gremmie/pelican-bootstrap3:
  Fix tag styles; add tag-0, de-duplicate tag-2.