
Effects:

     0: Pan position
        - Arg: Position (0 - 15)

     1: Arpeggio
        - Arg: Arpeggio args

     2: Note cut
        - Arg: Steps to wait

     3: Vibrato
        - Arg: Vibrato args

        Note that vibrato feels stronger for high pitched notes than for low
        pitched notes. This is because the vibrato is calculated using the
        period of the note, not the frequency. Both the Amiga and the GB use the
        period and add a delta to it for vigrato, which means that low
        frequencies are affected less than high frequencies:

        Low frequency note:  Period = 2000 +/- 20
        High frequency note: Period = 100 +/- 20

     4: Volume slide
        - Arg: Value to be written to the registers of the GBA.

     5: UNUSED

     6: UNUSED

     7: UNUSED

     8: Pattern jump
        - Arg: Pattern order to jump to

     9: Break + Set row
        - Arg: Row in next pattern (BCD): value = (arg & 0xF) + (arg >> 4) * 10

    10: Set speed
        - Arg: Speed (1 - 0xXX)

    11: UNUSED

    12: UNUSED

    13: UNUSED

    14: UNUSED

    15: Event
        - Arg: Event identifier

        This event doesn't have any effect in the music, but it can be used to
        trigger a callback to functions in the code of the user. For example, it
        can be used to synchronize the movement of some element of the
        background with the music, or to make enemies appear at some point of
        the song.
