Add a purpose for macroname, headername, enumname, globalname.
Ref #2153: There's still no documentation for methodname and classname.
These are actually defined in the docbook DTD for a different purpose so
I'm not sure how to deal with them.
http://www.docbook.org/tdg/en/html/methodname.html
http://www.docbook.org/tdg/en/html/classname.html