QDoc/Qt/Doxygen highlighting

[Felipe Lema]

Hi, everyone

I'm attaching a patch file to support highlighting in c++ as specified
in QDoc (which is the one Qt uses and Doxygen promotes).

I know Doxygen _supports_ Javadoc and that GTK documenting _looks like_
QDoc, however neither is quite the same.

More info here:
● http://www.stack.nl/~dimitri/doxygen/manual/docblocks.html#cppblock
● http://doc.qt.io/qt-5/qdoc-guide-writing.html

I hope this gets merged in.

Thanks
Felipe