Help: Configure copyright year automatically

Teach our Sphinx conf.py to compute the copyright end year
automatically.  Drop our hard-coded configuration for it.
Help: Configure |version| replacement correctly

Fix our configuration of the Sphinx conf.py 'version' entry to refer
to the correctly-spelled CMake_VERSION_(MAJOR|MINOR|PATCH) variables.
Help: Configure html page navigation bars

Add a small CMake logo to the left side of the header and footer
navigation bars.  Set the html theme, title, and short title explicitly.
Help: Configure html favicon
Merge topic 'doc-html-page-layout'

a023a26 Help: Configure html favicon
fb33219 Help: Configure html page navigation bars
e1f8196 Help: Configure |version| replacement correctly
edc7cc9 Help: Configure copyright year automatically