[LDCad] Rebrickable LDCad PBG export

[Orion Pobursky]

Now that I'm done with all 526(!) torso assembly entries (out of a possible 3700ish) in the cross reference file, I've moved the Set PBG generator out of experimental status. New url is:
https://www.ldraw.org/downloads-2/pbg-generator.html

and a new discussion thread started here:
https://forums.ldraw.org/thread-24060.html