Now all documentation is built using a separate port using
the --single-exec option of qdoc. This gaves significant speedup
as well as fixing quiet a few interlinking problems.
All -qch, -html and -docindex subpackages of Qt modules ports are
removed. The qt5-html and qt5-qch are now provided by x11/qt5/docs
instead of meta/qt5, thus REVISION set from the start.
This commit should fix problems with building Qt5 documentation
that people started seeing after switching to Clang. We also could
zap some interdependencies between Qt5 modules as well, but that's
a different story.