(updated 18/12/2014 urls from: https://gist.github.com/sj26/2600122)
Mac users: brew install gcc
curl https://gist.githubusercontent.com/charkost/cb4f5baeb6529f37218c/raw/d0331893dbae97ec63939e383f43d89b2ca838dc/rbenv.sh | sh && rbenv global 1.9.3-p194-perf