Updates on SSC to -ineqdeco- and -ineqdec0- (inequality indices, with decomposition by population subgroup)

[Stephen Jenkins]

With thanks as ever to Kit Baum (SSC maintainer), new versions of -ineqdeco- and -ineqdec0-. I've changed from using -gsort- to -sort- to speed things up with large datasets at the suggestion of Caspar Kaiser (thank you).