v9.4

Rework dulcimer music yet again, again

This edit combines what was dulcimer-tabs-dad.pdf and dulcimer-tabs-dgd.pdf
into a single file dulcimer-tabs-dxd.pdf. This contains TABs for all the
'D' tunes first (assuming D-A-D tuning) and all the 'G' tunes second
(assuming D-G-D tuning) in the same file.