Separate Ruby from Node, add basic Ruby role

Very basic, but it seems to be working. I've only tested on Ubuntu 12.04, but I've verified the package names for RedHat.

Wishlist:
- Ruby version management (rvm, rbenv, chruby, etc.)
- Compile Ruby from source (ruby-install or ruby-build)
- Rails

Unfortunately I'm not a Ruby guy, so I'm not sure what the best practices are for this.