Get ruby 2.0 on MacOSX via rbenv / ruby-build

Ruby 2.0 (2.0.0-p0) is out since yesterday, so we can now all run it.

If you already got rbenv installed, and ruby-build running via homebrew it is as easy as:

$ brew update && brew upgrade ruby-build
$ rbenv install 2.0.0-p0

Wait for it to compile and yay now running ruby 2.0!