Use newer Shellfu interface for handling usage errors

src/saturnin.sh.skel

         -K:*)   ig_mode=$1; ig_query=$2; shift 2; break ;;
         -S:*)   ig_mode=$1; ig_query=""; shift 1; break ;;
         -P:*)   ig_mode=$1; ig_query=""; shift 1; break ;;
-        .*:*)   warn "bad syntax: $*"; _saturnin__conf_usage ;;
+        .*:*)   _saturnin__conf_usage -w "bad syntax: $*" ;;
         *.*:*)  ig_mode=-e; ig_query=$1; shift 1; break ;;
-        --help:*) _saturnin__conf_usage -e 0                 ;;
-        *)      warn "bad syntax: $*"; _saturnin__conf_usage ;;
+        --help:*) _saturnin__conf_usage -e 0            ;;
+        *)      _saturnin__conf_usage -w "bad syntax: $*" ;;
     esac done
-    test -n "$ig_mode" || { warn "could not determine inigrep mode"; _saturnin__conf_usage; }
+    test -n "$ig_mode" || _saturnin__conf_usage -w "could not determine inigrep mode"
     debug -v ig_limit ig_query ig_mode Strategy
     if test -n "$*";
     then
     then
         files=("${ig_query%%.*}$SATURNIN_CONF_SUFFIX")
     else
-        warn "dunno what to load"
-        _saturnin__conf_usage
+        _saturnin__conf_usage -w "dunno what to load"
     fi
     debug -v files
     #shellcheck disable=SC2086
         --version)      saturnin__version;          exit  ;;
         -V|--version-semver) saturnin__get app-version ;;
         --saturnin-get-*) saturnin__get "$1"        ;;
-        -*)             saturnin__usage;            ;;
-        --*)            saturnin__usage;            ;;
+        -*)             saturnin__usage -w "unknown argument: $1" ;;
+        --*)            saturnin__usage -w "unknown argument: $1" ;;
         --)             shift; break                ;;
-        "")             saturnin__usage;            ;;
+        "")             saturnin__usage -w "too few arguments" ;;
         *)              break;                      ;;
     esac done
     subcommand="$1"; shift
     binpath+="$SATURNIN_LIBEXEC_PREFIX$subcommand"
     debug -v binpath
     debug "\$*='$*'"
-    test -x "$binpath" || {
-        warn "invalid sub-command: $subcommand"
-        saturnin__usage
-    }
+    test -x "$binpath" \
+     || saturnin__usage "invalid sub-command: $subcommand"
     SATURNIN_SUBCOMMAND="$subcommand" "$binpath" "$@"
 }
 

tests/cli/oracle/usage.stderr

   bar
   baz
   foo
+
+bad usage: too few arguments