Move usage() to saturnin.sh module

src/bin/satcmd.skel

 export SHELLFU_INIGREP_PATH SHELLFU_PATH SHELLFU_PRETTY_USAGE \
        SATURNIN_CACHE_HOME
 
-usage() {
-    mkusage "[-d|-v] command [args...]" \
-            "help" \
-            "--version"
-}
-
 main() {
     local subcommand
     while true; do case $1 in
         -v|--verbose)   export SHELLFU_VERBOSE=true; shift ;;
         --version)      saturnin__version; exit            ;;
         --version-semver) echo "$SATURNIN_APP_VERSION"; exit ;;
-        -*)             usage;                          ;;
-        --*)            usage;                          ;;
+        -*)             saturnin__usage;                ;;
+        --*)            saturnin__usage;                ;;
         --)             shift; break                    ;;
-        "")             usage;                          ;;
+        "")             saturnin__usage;                ;;
         *)              break;                          ;;
     esac done
     subcommand="$1"; shift

src/shellfu/saturnin.sh

     "$binpath" "$@"
 }
 
+saturnin__usage() {
+    mkusage "[-d|-v] command [args...]" \
+            "help" \
+            "--version"
+}
+
 saturnin__version() {
     #
     # Print version info