X11/xdg: migrate to XDG_CONFIG_DIR

.config/X11/xinitrc

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+# Run all system xinitrc shell scripts
+xinitdir="/etc/X11/xinit/xinitrc.d"
+if [ -d "$xinitdir" ]; then
+    for script in $xinitdir/*; do
+        echo "Loading xinit script $script"
+        if [ -x "$script" -a ! -d "$script" ]; then
+            . "$script"
+        fi
+    done
+fi
+
+source ~/.profile
+source $XDG_CONFIG_HOME/X11/xsession
+xrdb -merge $XDG_CONFIG_HOME/X11/xresources
+
+exec i3