code: def shift_argument
        if index = @entries.find_index { |type, _| type == :arg }
          entry = @entries[index]
          @entries.delete_at(index)
          entry.last
        end
      end
docs: @return [String] The first argument in the remaining parameters.
  
   @note   This will remove the argument from the remaining parameters.
  
   @example
  
     argv = CLAide::ARGV.new(['tea', 'white'])
     argv.shift_argument # => 'tea'
     argv.arguments      # => ['white']