could provide an option to get pedigree IDs as individual identifiers in VCF

[bhaller]

See discussion: https://groups.google.com/g/slim-discuss/c/7s7KiFEWj64/m/YEzo3S0bAAAJ. It would be convenient, if pedigree tracking is enabled, to be able to use pedigree IDs directly as the individual IDs in a VCF file.