wp_nav_menu parameter to print the menu description

[elvishp2006]

Currently, to print the description of any menu item is necessary write a Walker class and override the start_el method. I think it would be interesting to add a parameter in wp_nav_menu method to print the description automatically without the need to write a class for that. It would be something like this: print_menu_description => true

[obenland]

Duplicate of #29890.