2.1

Clefs, octaves and stems, as abcm2ps draws them.

A minor release. Notes are placed for the clef in force, clef changes part way through a
voice are drawn, octave= takes effect, and stems and beams follow abcm2ps's rules. The
model gains Event.clefChange. See Upgrading.

Clefs and octaves

• Notes follow the clef (#222). Every notehead, stem, ledger line, accidental, tie and
  slur used to be placed at its treble-clef position whatever clef the staff carried. Staff
  position is now counted from the clef's bottom line (ClefSpec.staffPosition(of:)). An
  octave clef (treble-8) moves nothing, as in abcm2ps.
• octave= on K: and V: (#224) shifts Note.pitch in the semantic pass, scoped as
  abcm2ps scopes it: a header K: covers every voice, a body K: or a V: its own voice,
  and each lasts until another octave= replaces it. Transposition.statesOctave lets
  octave=0 reset it.
• A K: with a clef and no key (#223). K:bass, K:clef=bass and [K:clef=bass] are
  read as options only (§3.1.14, §4.6) instead of being rejected. KeySignature records
  what was stated (statesKey, statesClef); what was left unsaid carries on from what is
  in force, so K:G after K:bass stays in the bass clef. An unreadable K: still warns,
  and now changes nothing.
• Clef changes are drawn (#223). A clef change part way through a voice is a new
  Event.clefChange where the field was written. A change against a bar line is a small
  clef before that bar (a courtesy clef at the end of a line, with the new clef full size
  at the head of the next); a change mid-bar is a small clef between the notes; a clef
  change alone draws no key signature. Measure.key is set only by a K: that names a key.

Stems and beams

• Only notes shorter than a quarter are beamed (#217), whatever the meter (§4.7). In
  6/8, 2/2 and 3/2, quarter notes were beamed to their neighbours.
• One stem direction per beam group (#218). Each group's direction is decided before
  any of it is drawn: down where the highest note is farther above the middle line than the
  lowest is below, up in the opposite case, and a group as far above as below follows the
  part's previous stem (up if none). Every stem in the group is placed for that direction.
• A middle-line note follows the stem before it (#221) in an .auto voice, across bar
  lines and rests, and stems up where there is none. stem=, pipe format and a shared
  staff's opposition still decide outright.

What's Changed

• Fix #217 — don't beam notes too long to carry a flag by @sbeitzel in #219
• Fix #218 — one stem direction per beam group, every stem placed for it by @sbeitzel in #220
• Fix #222, #224 — place notes for the clef in force; apply octave= by @sbeitzel in #225
• Fix #221 — stem a middle-line note the way the stem before it went by @sbeitzel in #226
• Fix #223 — accept a K: that names a clef but no key, and draw clef changes by @sbeitzel in #227
• Release 2.1.0 by @sbeitzel in #228

Full Changelog: v2.0.0...v2.1.0

Upgrading

Event has a new case, clefChange(ClefSpec). An exhaustive switch over Event needs a
branch for it; everything else is source-compatible with 2.0.0. The new KeySignature and
Transposition initializer parameters have defaults.

Engraved output changes for tunes in a clef other than treble, tunes using octave=, beamed
quarter notes in compound meter, and some stem directions on beam groups and middle-line
notes. Each now matches abcm2ps 8.14 -g.