QB4ST final issues

Hi Rob

I've edited section 6.4 of QB4ST to insert a short note about the intention
to add an example here in future - but have left that section there, so no
numbering changes arise.

There are still 2 open issues in the document:

ISSUE 129
Insert appropriate form of reference to SDW work if available to fill this
gap

If I remember correctly, that was there in case some of the work on
Geosparql extensions went far enough to define the kinds of base spatial
concepts you had in mind.

Since that hasn't yet got to the point of a formal document we could refer
to, then I'm guessing this issue should just be removed, because there
isn't yet a suitable reference.

I'm happy to make that change, but do I understand correctly what you
intended?

Thanks

Bill