Add "docinfo" table to IPython Notebook posts

Ah, the mysteries of the last hour or two are now explained: the HTML
sitting live on my web site was produced by an updated version of
"cache-text" which apparently never got checked in from my travel
laptop.  So I found the repository, copied the changes over here to my
main laptop, and can now formally commit this wonderful consolidation of
"docinfo" table templates and logic.  And "bin/diff" now shows only the
changes that I would expect, so I can proceed with further web site
updates and improvements.