Accept negative numbers for group and off_by

[kinwie]

The specs didn't mention it but negative numbers for group and off_by works in rgc sfz, Cakewalk DropZone, DimPro, Rapture, sforzando and BassMidi.

Example:

<region>
sample=*sine
key=60
group=218
off_by=-218

<region>
sample=*silence
key=62
group=-218

[alcomposer]

After some testing- Sforzando allows text to be entered as well:

<region>
sample=*sine
key=60
group=218
off_by=text

<region>
sample=*silence
key=62
group=text

[paulfd]

It's actually nice to have text. Could we cheat by hashing whatever is given in here? This would probably be too weird for users in case of a collision.

[alcomposer]

Yeah, I don't think there is an issue to use chars. I wonder if there are any other opcodes that have similar behaviour?

My tests so far:	Player	off_by format
Sforzando	Char -> atof() (invalid input = 0.0)
DropZone	Signed Integer

[alcomposer]

After more testing- Sforzando does use Char, but as @jpcima suggested in PM, atof().

This example switches off each C independently:

<region>
sample=*sine
key=60
group=20
off_by=1
<region>
sample=*silence
key=62
group=1

<region>
sample=*saw
key=48
group=10
off_by=2
<region>
sample=*silence
key=50
group=2 

While in this example- both C's get switched off by either D:

<region>
sample=*sine
key=60
group= 218
off_by=hello_world   //atof() makes this string 0.0
<region>
sample=*silence
key=62
group=hello_world   //atof() makes this string 0.0

<region>
sample=*saw
key=48
group= 200
off_by=hello_world_2   //atof() makes this string 0.0
<region>
sample=*silence
key=50
group=hello_world_2   //atof() makes this string 0.0