First attempt at DocBook V5.1-CSPRD01

Hi folks,

Attached, please find a ZIP file containing my first attempt at
DocBook V5.1 CSPRD01. Feedback welcome. Chet, if you would be so kind
as to double-check that I've crossed all the correct OASIS i's and
dotted all the t's, I'd really appreciate that.

If the ZIP doesn't come through, you can get it here:

   http://nwalsh.com/scratch/docbook-v5.1-csprd01/

Assuming my attempt passes muster, I think we should vote to make this
a Committee Specification tomorrow. Or whatever the OASIS process calls
the official thing now.