def create_option(flag, argument = nil)
      return '' unless flag
      flag = flag.to_s
      return " #{argument}" if flag == 'extra'
      set_pandoc_ruby_options(flag, argument)
      if !argument.nil?
        "#{format_flag(flag)} #{argument}"
      else
        format_flag(flag)
      end
    end
def create_option(flag, argument = nil)
      return '' unless flag
      flag = flag.to_s
      return " #{argument}" if flag == 'extra'
      set_pandoc_ruby_options(flag, argument)
      if !argument.nil?
        "#{format_flag(flag)} #{argument}"
      else
        format_flag(flag)
      end
    end
Takes a flag and optional argument, uses it to set any relevant options
 used by the library, and returns string with the option formatted as a
 command line options. If the option has an argument, it is also included.