Merge branch 'async' into dev

src/include/66/constants.h

src/include/66/svc.h

src/lib66/ssexec_help.c

src/lib66/ssexec_start.c

src/lib66/ssexec_stop.c

src/lib66/ssexec_svctl.c

src/lib66/svc_init_pipe.c

src/lib66/svc_send.c