* Rhythmic_head, Staff_symbol, Grace_align_item, Break_align_item,
Bar, Span_bar are now interfaces, Staff_bar was removed. Use a
callback for determining barsize.
* Rhythmic_head, Staff_symbol, Grace_align_item, Break_align_item,
Bar, Span_bar are now interfaces, Staff_bar was removed. Use a
callback for determining barsize.