Gap specification in key model

[lifthrasiir]

Inspired from Hitkey's diary entry:

• It is possible to reuse #xxx[1-2][A-Z] which is normally unused by BMS files as a spacer for layout.
  • Separator between 1P and 2P, scratch on the right hand side, 10KEYS:
    angolmois -w -K '11a 12b 13a 14b 15a 16s 1Zs' '21a 22b 23a 24b 25a 26s'
  • Separator between 1P and 2P, 14KEYS:
    angolmois -w -K '16s 11a 12b 13a 14b 15a 18b 19a 1Zs' '21a 22b 23a 24b 25a 28b 29a 26s'
  • Simulated Couple Play rendering for Double Play charts using #PLAYER 3:
    angolmois -w -B -K '11a 12b 13a 14b 15a 16s 1Aa 1Bs 1Cs 1Ds 1Es 1Fs 1Gs 1Hs 1Is 1Js 1Ks' '21a 22b 23a 24b 25a 26s'
• I also wish these options:
  • --no-combo: No combo display
  • --half: Half-line display (* each lane overlaps with previous/next lanes by half the lane width)

It would be good to have an explicit "gap" specification in --key-spec:

Example 1: angolmois -w -K '11a 12b 13a 14b 15a 16s' '(40) 21a 22b 23a 24b 25a 26s'
Example 2: angolmois -w -K '16s 11a 12b 13a 14b 15a 18b 19a' '(40) 21a 22b 23a 24b 25a 28b 29a 26s'
Example 3: angolmois -w -B -K '11a 12b 13a 14b 15a 16s' '(450) 21a 22b 23a 24b 25a 26s'

If we are careful enough, --half can be simulated as follows:

--key-spec '11a (-12) 12b (-12) 13a (-12) 14b (-12) 15a 16s'