Allowed for nil display_method_name.
Fixed multi-column division of elements.
Fixed calculation of number of entries per column.
Moved display_method_name into the options.
Fixed listy_links with no css class specified.
Changed display_method_name to display_method.
Allowed nil display_method in listy_tree.
Fixed listy_tree display_method call.
Updated README to reflect new display_method.