Warnings are errors on clang

We were setting -Wall -Werror when compiling with GCC to make sure that
we get rid of all compiler warnings as part of the standard build/test
process.  Now we do that for clang, too, for when we're developing on
Mac OS X.
Build man pages based on release date

We build the man pages for a repo based on a release date now, which
greatly simplifies the process.  The extra benefit is compiled man
pages are now consistent across all installations instead of dated
based on when a repo was built.
Merge branch 'feature/man-pages' into c-template

* feature/man-pages:
  Build man pages based on release date
Fatal warnings with Intel compiler

We want -Wall and -Werror with Intel's compiler, too.
Don't install empty man page directories

The CMake logic for installing man-page link files would create a
directory for each section that might possibly contain links.  Now it
only creates directories for the sections that actually contain links.
This also fixes a bug when using CMake 2.6, where the docs/links
directory needed to be present, even if your project has no links
whatsoever.  It's now fine for the directory to be missing.
Explicit header and footer in man pages

You now need to explicitly provide the text that goes in the header and
footer of each man page.  We were relying on a pandoc default before,
but that default has changed recently, so now we're requiring you to
provide specific text.
Remove old Sphinx documentation template

To complete the move to man page documentation.
Merge branch 'feature/docs' into c-template

* feature/docs:
  Remove old Sphinx documentation template
  Explicit header and footer in man pages
  Don't install empty man page directories
Update to latest libcork API
Merge remote-tracking branch 'template/c-template' into develop

* template/c-template:
  Remove old Sphinx documentation template
  Explicit header and footer in man pages
  Don't install empty man page directories
  Fatal warnings with Intel compiler
  Build man pages based on release date
  Warnings are errors on clang