[MIXLIB-30] Malachheb 1.4.0

I added the argument 'in' to specify the valid values ​​of an option like this : 

    option :log_level,
      :description => "Set the log level (debug, info, warn, error, fatal)",
      :in => ['debug', 'info', 'warn', 'error', 'fatal']

I think this feature is important for some options,
Thanks.
This code won't get run because of the raise.