Add -h to enable overriding definition of "hidden"

src/bin/sfdoc

             "-O, --object       Treat MODULE as function or variable"   \
             "                   name and find respective module first." \
             "-d, --debug        Turn on debugging"                      \
+            "-h, --hide REGEX   Use REGEX to determine what is hidden." \
+            "                   (See also -a and 'sfdoc sfdoc'.)"       \
             "-a, --all          Don't ignore hidden (starting with"     \
             "                   underscore) modules or objects"         \
             "--encoding ENC     Override encoding of the source text"   \
         -O|--object)    spectype=obj;               shift ;;
         -d|--debug)     PRETTY_DEBUG=true;          shift ;;
         -a|--all)       SFDOC_SHOW_HIDDEN=true;     shift ;;
+        -h|--hide)      SFDOC_SHOW_HIDDEN=false; SFDOC_HIDE_REGEX="$2"; shift 2 || usage -w "no REGEX?" ;;
         -I|--include)   SHELLFU_PATH="$2:$SHELLFU_PATH"; shift 2 || usage -w "no PTH?" ;;
         -s|--src)       action=src;                 shift; break ;;
         -l|--ls)        action=lsx;                 shift; break ;;