using LyricHyphens in the docs

[Mark Polesky]

I think the "Salve, "Regína" example in NR 2.8 "Ancient Notation"
would be improved by using LyricHyphens. For example, instead of
"Sal- ve, Re- gí- na," use "Sal -- ve, Re -- gí -- na,".

Unless there's some ancient hyphen typesetting convention that I
don't know about.  The file involved is
input/manual/ancient-headword.ly. There may be others, but I just
noticed it there.

Anyone care to comment on that?
- Mark