Rename saturnin_meta module

Since saturnin's dedication to be "meta-command" builder, the distinction
between "meta" and something else does not make much sense.

mkit.ini

     src/libexec/satcmd-echo     = satcmd-echo
 
 [files:share]
-    src/shellfu/saturnin_meta.sh = shellfu/saturnin_meta.sh
+    src/shellfu/saturnin.sh     = shellfu/saturnin.sh

src/bin/satcmd.skel

 # =====END BUILT PART=====
 #
 
-shellfu import saturnin_meta
+shellfu import saturnin
 
 export SHELLFU_INIGREP_PATH SHELLFU_PATH SHELLFU_PRETTY_USAGE \
        SATCMD_VERSION SATCMD_CACHE_HOME