add "behaviour 3", which opens link on click, expands menu on arrow click

Great library -- thank you for your work! We wanted our tablet menus to open the link on click and expand the menu when the user clicks an arrow next to the link. I added this to the Drupal module as "behaviour 3", and will submit a patch to the module on drupal.org after I submit this.
https://www.drupal.org/node/2354373

Thanks again for your work. Everything works great -- I just thought this might be useful to other folks as well.