parser.yy: remove unused CHORDMODIFIER_PITCH and CHORDMODIFIERS
stencil.scm: \hspace is not special in fill-line;issue 3504
key-signature: restore function for LilyJAZZ.ily; issue 3606

key-signature-interface::alteration-position
Issue 3618/1: Eliminate EXPECT_PITCH token in parser
Issue 3618/2: Parser: replace is_duration with more versatile make_duration function
Issue 3618/3: Eliminate EXPECT_DURATION token in parser
Issue 3618/4: big rewrite of optional argument scanning.  See comment inside.
Merge branch 'issue3618' (early part) into staging

Not sure whether every state in between will perfectly bisect, so
using a merge commit.
Parser: remove unused operator priorities
EG: Some updates on music functions