GeoShape and GeoCoordinates should allow a postalCode [edit: + country] for rough positioning. #810
Description
Sub-issue of #113.
This is non-essential in that we can use GeoShape --address-- PostalAddress -- postalCode-- xyz.
But that is needlessly heavy, so let's pick out the most useful piece of PostalAddress for this purpose, postalCode. This fits well with the approach implemented in #808 which allows these to have a simple textual 'address' too.