Update to Bach BWV 988 aria

Bar 6: correct 2nd bass dotted quarter note, beat 2.5->beat 2
Bar 18: correct e->g in last eight note in treble
(Steve Shorter)
update to v2.16.1
minor cosmetics
Bar 21: add prallup to first treble note
Bar 23: add prallup to the 'a' in first voice
(Javier Ruiz-Alma)
Close #12