GitLab

Add helper function to list gems in a pretty way (only with rvm, for now). Add
missng EOF newline and a todo to the ruby plugin.

Add helper function to get rvm head. Add helper function to link zsh
completion that comes with rvm into om-my-zsh plugin directory, but don't
overwrite the completion that comes with oh-my-zsh (oh-my-zsh's completion is
better, but I want to be able to compare).

Add alias to list installed rubies. Add alias to list gemsets in active ruby.

Add helper functions to switch gemsets on ruby-1.8.7-p334 and ruby-1.9.2-p180.
Add completion definitions for helper functions.