Update to Ruby 2.1.2 and rebuild bundle

After updating to Ruby 2.1.2 (chruby doing an excellent job as always),
I decided to discard a lot of dependencies that I wasn't using on my own
system, like Gollum and Jekyll.

After doing this, I realized nanoc was the only major root node in my
gem dependency graph (thanks, rgdg). So I decided to rebuild the bundle
from scratch, with only Rouge supported. Once the next nanoc is out, we
can finally upgrade to Rouge and abandon Python-from-Ruby for good.

Pry requires CodeRay, so for now, CodeRay is still available as a
highlighter. Again, I am moving to Rouge once support is released.