X11: Add .xinitrc

This is just a slightly refactored version of /etc/X11/xinit/xinitrc.

.xinitrc

@@ -0,0 +1,23 @@
+#!/bin/sh
+
+sysresources=/etc/X11/xinit/.Xresources
+sysmodmap=/etc/X11/xinit/.Xmodmap
+userresources="$HOME"/.Xresources
+usermodmap="$HOME"/.Xmodmap
+
+[ ! -f "$sysresources" ] || xrdb -merge "$sysresources"
+[ ! -f "$sysmodmap" ] || xmodmap "$sysmodmap"
+
+[ ! -f "$userresources" ] || xrdb -merge "$userresources"
+[ ! -f "$usermodmap" ] || xmodmap "$usermodmap"
+
+unset {sys,user}{resources,modmap}
+
+if [ -d /etc/X11/xinit/xinitrc.d ] ; then
+	for f in /etc/X11/xinit/xinitrc.d/?*.sh ; do
+		[ ! -x "$f" ] || . "$f"
+	done
+	unset f
+fi
+
+exec i3