more doxygen markup

src/or/buffers.c

src/or/command.c

src/or/connection_or.c

src/or/cpuworker.c

src/or/directory.c

src/or/dirserv.c

src/or/dns.c

src/or/main.c

src/or/rendclient.c

src/or/rendcommon.c

src/or/rendmid.c

src/or/rendservice.c

src/or/router.c

src/or/routerlist.c