Adds win+left or win+right to switch tag

This involved the patch from here:

https://lists.suckless.org/dev/1104/7590.html

I use this on the pinephone with win+left and win+right bound to a swipe
left or right on the bottom edge of the screen

config.def.h

@@ -195,6 +195,8 @@ static Key keys[] = {
 	{ 0,                            XF86XK_AudioMute,          0,         spawn,          {.v = volumeToggle } },
 	{ 0,                            XF86XK_MonBrightnessUp,    0,         spawn,          {.v = brightnessUp } },
 	{ 0,                            XF86XK_MonBrightnessDown,  0,         spawn,          {.v = brightnessDown } },
+	{ MODKEY,                       XK_Right,                  0,         shiftview,      {.i = 1 } },
+	{ MODKEY,                       XK_Left,                  0,         shiftview,      {.i = -1 } },
 	// On the pinephone, I want a single press of the power button to put the phone in sleep mode.
 	// I want a double press to toggle the keyboard
 	// I want a hold press to bring up the power menu

dwm.c

@@ -221,6 +221,7 @@ static void setlayout(const Arg *arg);
 static void setmfact(const Arg *arg);
 static void setup(void);
 static void seturgent(Client *c, int urg);
+static void shiftview(const Arg *arg);
 static void showhide(Client *c);
 static void sigchld(int unused);
 static void spawn(const Arg *arg);
@@ -1873,6 +1874,26 @@ seturgent(Client *c, int urg)
 	XFree(wmh);
 }
 
+/** Function to shift the current view to the left/right
+ *
+ * @param: "arg->i" stores the number of tags to shift right (positive value)
+ *          or left (negative value)
+ */
+void
+shiftview(const Arg *arg) {
+	Arg shifted;
+
+	if(arg->i > 0) // left circular shift
+		shifted.ui = (selmon->tagset[selmon->seltags] << arg->i)
+		   | (selmon->tagset[selmon->seltags] >> (LENGTH(tags) - arg->i));
+
+	else // right circular shift
+		shifted.ui = selmon->tagset[selmon->seltags] >> (- arg->i)
+		   | selmon->tagset[selmon->seltags] << (LENGTH(tags) + arg->i);
+
+	view(&shifted);
+}
+
 void
 showhide(Client *c)
 {