Add --saturnin-get-saturnin-version

src/saturnin.sh.skel

     local key=${1#--saturnin-get-}      # internal info key
     case "$key" in
         saturnin-conf-path) echo "$SATURNIN_CONF_PATH"      ;;
+        saturnin-version)   echo "__MKIT_PROJ_VERSION__"    ;;
         app-git-hash)   echo "$SATURNIN_APP_GIT_HASH"       ;;
         app-version)    echo "$SATURNIN_APP_VERSION"        ;;
         cache-home)     echo "$SATURNIN_CACHE_HOME"         ;;