3Simai feature support

The following are 3Simai features that MaiConverter currently supports. Checklist based from xen0n's maidata-rs

Metadata field support

Field	Parse support	Implementation details
title	✔️	SimaiTransformer returns the value but it's only used in parse_file_str function
artist	✔️	SimaiTransformer returns the value but it's never used
level	✔️	SimaiTransformer returns the value but it's only used in parse_file_str function
chart	✔️	See list below
smsg	✔️	Ignored
des	✔️	Ignored
freemsg	✔️	Ignored
first	✔️	Ignored
wholebpm	✔️	Ignored
amsg_first	✔️	Ignored
amsg_time	✔️	Ignored
amsg_content	✔️	Ignored
PVStart (MaiPad PLUS extension)	✔️	Ignored
PVEnd (MaiPad PLUS extension)	✔️	Ignored
demo_seek (MaiPad PLUS extension)	✔️	Ignored
demo_len (MaiPad PLUS extension)	✔️	Ignored

Chart feature support

• BPM (float)
• beat divisor {float}
  • normal {float}
  • absolute duration {#float}
• end mark E
• TAP B,
  • simplified BOTH/EACH TAP form (16 38 etc.; 123 and such are also allowed)
  • BREAK modifier Bb
  • EX modifier Bx, Bex
  • star-shape modifier B$, Bb$, B$b, B$$,
• HOLD Bh[length],
  • EX modifier Bxh[length], Bex[length]
  • normal duration [x:y]
  • absolute duration [#float]
  • instant hold note Bh, Bh[0:0]
• SLIDE FxE[length],
  • all track pattern - ^ < > v p q s z pp qq V w
  • multiple tracks sharing one start 1-3[4:1]*-4[4:1]
  • BREAK modifier 1b-3[4:1],
  • EX modifier 1x-3[4:1], 1ex-3[4:1],
  • tapless modifiers ? ! $
  • star tap note to regular tap note modifier @
  • arbitrary slide delay FxE[BPM#length]
  • absolute duration
    • [#1.5]
    • [160#2]
    • [3##1.5]
  • instant slide note 1-3[0:0]
• BOTH/EACH note/note,
  • arbitrary number of concurrent notes allowed
  • pseudo both/each note`note
  • both/each with fake note 3/0