Doxy­gen stuff updat­ed in 9‑current

I com­mit­ted my patch for tools/kerneldoc/subsys. Except for not gen­er­at­ing the PDF part, this is now the same con­fig which I use to gen­er­ate the online ver­sion. While writ­ing the com­mit log I noticed that I did more changes than I thought…

So any­one who wants to gen­er­ate the Doxy­gen docs of some FreeB­SD ker­nel sub­sys­tems on his own, can do it now. Adding more sub­sys­tems is easy, just make a copy of one the the exist­ing Doxyfile-* files – keep the same nam­ing scheme – and change the con­tents. Every­thing else is han­dled automatically.

I also added a link to the FreeB­SD wiki. It is not at a promi­nent place (near the end of the main page), but at least some­one can find the link to the my FreeBSD-doxygen page there.