[CDG5] Rez compression info (macresources)

[Elliot Nunn]

Yes, still hacking on macresources...

Anyone object to this syntax for stuffing compression info into Rez
files? The C preprocessor hash-pragma mechanism is intended for exactly
this kind of implementation-specific functionality. And because Rez can
read some C header files, it can also handle pragmas (by ignoring them).

Previously I have tried structured comments, but I find them inelegant.

The "sys7" part explicitly reminds the user that earlier Systems cannot
access these structures.

```
#pragma sys7_compress GreggyBits
data 'foo ' (0) {
	$"ABCD"
}
#pragma sys7_compress off
```