drastic measure to squeeze Rachmaninoff Op23/2 into less pages

Use Y-extent hack to fool extent estimation, and add several potential
system break points so that some bars are packed more closely. Also fix
some curves and dynamic text positioning due to break point change.
Sync A4/Letter layout of Rachmaninoff Op.23/3

It was a surprise that letter and a4 have different line breaks, causing
major headache for dynamics / hairpin positioning. Make them equal so
tuning becomes easier. Not much left to tune.
Also compress pages for letter size of Rachmaninoff Op.23/2

Previous page-compression tuning was only effective for A4 size paper,
while letter sized on still stays at 8 pages. Now fixed.
More realistic MIDI for Rachmaninoff Op.23/2, and more cleanup

MIDI is a bit closer to real performance with hidden tempo, dynamics and
hairpins on each staff, as well as redefined MIDI volume.
Globally replace accent with smaller version.
Editorial changes added to file top section (in addition to existing
inline comments) to explain differences between editions.
Compress accidentals on certain bars so it doesn't look too crowded.
Even more curve tuning.
Show/hide fingering function now replaced by tags.
Remove all fingerings from 2nd occurrence of main theme.
Fix composition year
MIDI overhaul for Rachmaninoff Op. 23/3

Tons of hidden dynamics / hairpin so that MIDI volume is more realistic
MIDI overhaul for Rachmaninoff Op. 23/1

Tons of hidden control for more realistic midi volume. And use
\barNumberCheck everywhere.
Handle repeated section in MIDI for 3rd prelude

Split another \score section specifically for handling repeat of first
section for Rachmaninoff Prelude Op. 23/3.
Merge branch 'rachmaninoff-prelude23-fixes' of https://github.com/abelcheung/The-Mutopia-Project
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