OK, on looking at that PDF document - the way they handle key signatures is butt-ugly. What I'd hoped is that somebody night have extended it to handle the sort of microtonal key signatures you get in Turkish music, this kind of thing:

http://neyzen.com/nota_arsivi/02_klasik_eserler/082_segah/incecikten_bir_kar_yagar_ney.pdf

where the backwards flats indicate one comma flat of the corresponding "natural". But while ABC could be extended to do that without major chaos, it's completely alien to the Lilypond model.