Autodetect visitation return type for unary visitors (refs svn #10837)
Autodetect visitation result type for binary visitors (refs svn #10837)
Make sure that we do not occasionally disable variadic templates for Clang (refs trac #Clang compiler defines GNUC)
Removed deprecated advice (refs trac #10273)
Simplify Multi visitation section in Tutorial (refs trac #10653)
Added missing relational operators and their docs (refs trac #10811 and #8620)