Feature/deletelistvenue

I was having trouble removing items from a list, and wasn't able to remove venues from a list (see http://stackoverflow.com/questions/17347837/ruby-on-rails-foursquare-remove-list-item-gives-400-value-is-invalid-for-item-i), so I expanded the delete_list_item method to take an options param, allowing removal of an item, venue, or tip.