def register(command, action_class, description)
      mapping[command] = ActionConfig.new(action_class, description)
    end
def register(command, action_class, description)
      mapping[command] = ActionConfig.new(action_class, description)
    end
Register a new command/action to be available to the CLI

 @param command [String] the string that a user will type to execute the
   action, e.g. "help" for the command the will print out help info.
 @param action_class [Class] the class that will execute the logic for
   the given command.