Improve the readme a bit
Use strings for modes for Ruby 2
Add supported platforms to metadata
Support all RHEL 5.X releases and switch to yum-epel

value_for_platform is great except you can’t use version ranges so you
have to add every possible RHEL 5 release.  Switch to a case statement
to avoid that.  Also use yum-epel since yum::epel is no more