List Simple list class. A simple list class used internally. @world: @Returns: @list: @list: @list: @data: @Returns: @list: @data: @Returns: @list: @Returns: @list: @Returns: @list: @data: @Returns: @list: @data: @Returns: @list: @Returns: @list: @equals: @list: @Returns: @list: @fn: @user_data: