refactor for maintainability
Gemfile update
include @media rules in the selector count

* I checked the fixture files in blesscss and it seems to count them, so
  I will too
update a copied spec context
add a spec to ensure @charset isn't counted
@font-face should count as a selector

* according to blesscss anyway
percentages inside @keyframes should count as a selector

* according to blesscss anyway