Try to be more conformant with XDG standards

First attempt to base saturnin paths on XDG paths.

mkit.ini

 
 [ENV]
     PREFIX = /usr/local
+    XDG_DATA_HOME = $HOME/.local/share
+    XDG_CACHE_HOME = $HOME/.cache
+    XDG_CONFIG_HOME = $HOME/.config
 
 [roots]
     bin     = [ENV:PREFIX]/bin
     etc_bc  = /etc/bash_completion.d
 
 [tokens]
-    __SATURNIN_CACHE_HOME__     = $HOME/.cache/saturnin-demo
-    __SATURNIN_CONFIG_USER__    = $HOME/.saturnin-demo
+    __SATURNIN_DATA_HOME__      = [ENV:XDG_DATA_HOME]/saturnin-demo
+    __SATURNIN_CACHE_HOME__     = [ENV:XDG_CACHE_HOME]/saturnin-demo
+    __SATURNIN_CONFIG_HOME__    = [ENV:XDG_CONFIG_HOME]/saturnin-demo
     __SATURNIN_CONFIG_LOCAL__   = [roots:etc]
     __SATURNIN_LIBEXEC__        = [roots:libexec]
     __SATURNIN_SHARE__          = [roots:share]
+    __SATURNIN_SHELLFU_DIR__    = [roots:share]/shellfu
 
 [modes]
     bin     = 755

src/bin/app.skel

     SATURNIN_APP_VERSION="__MKIT_PROJ_VERSION__"
     SATURNIN_APP_GIT_HASH="__MKIT_PROJ_GIT_LASTHASH__"
     SATURNIN_CACHE_HOME="__SATURNIN_CACHE_HOME__"
+    SATURNIN_CONFIG_HOME="__SATURNIN_CONFIG_HOME__"
+    SATURNIN_DATA_HOME="__SATURNIN_DATA_HOME__"
     SATURNIN_LIBEXEC="__SATURNIN_LIBEXEC__"
     SATURNIN_LIBEXEC_PREFIX="__MKIT_PROJ_PKGNAME__-"
+    SHELLFU_PATH="__SATURNIN_SHELLFU_DIR__"
     PRETTY_USAGE="subcommand"
 }
 
 
 SATURNIN_CONF_PATH="$(
     saturnin__conf_mkpath \
-        __SATURNIN_CONFIG_USER__/ini.d \
-        __SATURNIN_CONFIG_USER__ \
+        __SATURNIN_CONFIG_HOME__/ini.d \
+        __SATURNIN_CONFIG_HOME__ \
         __SATURNIN_CONFIG_LOCAL__ \
         __SATURNIN_SHARE__/ini.d
 )"
 #
 
 export SATURNIN_CONF_PATH SHELLFU_PATH PRETTY_USAGE \
-       SATURNIN_CACHE_HOME
+       SATURNIN_CACHE_HOME SATURNIN_CONFIG_HOME SATURNIN_DATA_HOME
 
 saturnin__main "$@"