dropdown() bug fix and improvement - parent menu item can have link and other properties

[douglassdavis]

Can now pass in properties for parent menu item in dropdown() instead of just title, order and attributes. That way, the parent menu item can link to somewhere as well.

if three arguments are passed in to dropdown(), code was assuming that 3rd arguments is attributes and assigning the $order parameter to $attributes. When there are three arguments, 3rd argument could really be order with attributes not passed in at all.

Fixes #68 Fixes #67