Since BoostBook stylesheets were updated to pass through Doxygen anchor
names to BoostBook output, references from QuickBook and manually
written BoostBook docs were broken. Fix this by using classref/classname
and similar tools to reference Doxygen-generated content.
Also, to avoid anchor clashes between different parts of Boost.Utility
docs, use proper anchor namespacing: avoid using manual anchors where
possible and use fully qualified namespace where not.
Fixes https://github.com/boostorg/utility/issues/110.
