Reverted the Doxygen-related change made earlier
Reverted the Doxygen-related change made earlier

It turns out that I had already added doc generation for the private
API, but it had to be explicitly enabled with a CMake option.  I've
reverted the change, and while I'm at it, I made a slight improvement to
the option name.

kyllingstad/coral,kyllingstad/coral,viproma/coral