notes:
- when offset is given as token+constant, take the offset of the *last* byte of
  the token rather than the first when calculating the offset
- everything is in little endian; jukebox gold was made for 8086

instrument
offset    | size     | token | description
----------|----------|-------|--------------------------------------------------
        0 |        3 |       | flags uuuuuuuu uuuuuuuu uuuuuuuf
          |          |       | u - unknown
          |          |       | f - instrument is a pcm sample. if unset, the
          |          |       |     instrument is found in opl3.bnk (? TODO)
        3 |       11 |       | null padded instrument name

adlib instrument
offset    | size     | token | description
----------|----------|-------|--------------------------------------------------
        0 |       28 |       | 0xAA repeated
       28 |       28 |       | unknown (possibly opl3 parameters?)

main header
offset    | size     | token | description
----------|----------|-------|--------------------------------------------------
        0 |       27 |       | ascii signature '>>> VC2, (C) ADLIB INC <<<\x0E'
       27 |        1 |       | always 0
       28 |        1 |       | unknown
       29 |        3 |       | always 0, 2, 0
       32 |        2 |       | unknown, likely tempo?
       34 |        1 |       | unknown
       35 |        2 |       | always 1, 0
       37 |        1 |       | unknown
       38 |        2 |       | always 0
       40 |       24 |       | unknown
       64 |       22 |       | 0x7F repeated
       86 |       40 |       | null padded song name
      126 |        1 |       | unknown
      127 |        2 |       | always 0xFFFF
      129 |       23 |       | always 0
      152 |        2 |       | unknown
      154 |        2 |       | size of song data
      156 |      274 |       | unknown
      430 |        2 |    is | number of instruments
      432 |  [is]*14 |    it | instrument table
     it+1 |   itn*56 |   ait | adlib instrument table. itn is calculated as the
          |          |       | number of instruments that do not have flag f set
    ait+1 |