MOD, S3M, XM, and IT uses different numbers to represent different commands.
JGMOD convert these different commands in to protracker like commands.
Command 0-15 are protracker effects. Others are S3M extended effects.

Below are the list of JGMOD commands supported. As more effects supported
by JGMOD, I will update the list. This is good for my own reference.

Command
-------

0       Arpeggio. Use by MOD. Unsupported yet.
1       Pitch slide up. Use only by MOD.
2       Pitch slide down. Use only by MOD.
3       Slide to note. MOD and S3M.
4       Vibrato. MOD and S3M.
5       Slide to note + Volume slide. MOD only
6       Vibrato + volume slide. MOD only
7       Tremolo. Unsupported yet.
8       Set panning.  MOD and S3M
9       Set sample offset. MOD and S3M
10      Volume slide. MOD only
11      Position Jump. MOD and S3M
12      Set Volume. MOD only
13      Pattern Break. MOD and S3M
14      Extended command. See below
15      Set tempo and bpm. MOD only.

16      Set tempo. S3M only
17      Volume slide. S3M only
18      Porta Down. S3M only
19      Porta Up. S3M only
20      Tremor. S3M only
21      Vibrato + Volume Slide. S3M only.
22      Portemento to note + volume slide. S3M only.
23      Retrig + volume slide. Not supported yet.

25      Set bpm. S3M only
26      Fine vibrato. S3M only
27      Set Global volume. S3M only

Extended command
----------------
1       Fine slide up. MOD only
2       Fine slide down. MOD only
3       Set glissando. Not supported yet
4       Set vibrato waveform. MOD and S3M
5       Set finetune. MOD and S3M 
6       Loop pattern. MOD and S3M
7       Set tremolo waveform. Not supported yet.
8       Set 16 positon panning. MOD and S3M
9       Retrigger sample. MOD only
10      Fine volume slide up. MOD only
11      Fine volume slide down. MOD only
12      Cut sample. MOD and S3M
13      Delay Sample. MOD and S3M
14      Delay pattern. MOD and S3M

16      Stereo Control (S3M only)


