update rbenv.zsh according to manpage
Merge pull request #123 from victorklos/rbenv_inclusion_per_docs

update rbenv.zsh according to manpage
Update the me method for general use
Only call rbenv init if installed
Merge pull request #126 from jacobwg/no-fail-without-rbenv

Only call rbenv init if installed
Merge pull request #125 from jacobwg/generalize-irbrc

Update the me method for general use
Merge remote-tracking branch 'holman/master'