Truly toggle between tiled and fullscreen

I don't know why I couldn't implement it before, but now that I know
more about shell scripting, I know that this works. There's an even
better solution I found in the bspc man pages, which will be covered
in the next commit.

.config/sxhkd/sxhkdrc

@@ -92,10 +92,11 @@ super + r
 
 # Toggle between tiled and "true" fullscreen
 super + t
-    bspc node focused -t fullscreen
-
-super + shift + t
-    bspc node focused -t tiled
+    if [ -z "$(bspc query -N -n focused.fullscreen)" ]; then \
+        bspc node focused -t fullscreen; \
+    else \
+        bspc node focused -t tiled; \
+    fi
 
 # Toggle between floating and tiled (default)
 # This is the equivalent of a floating window in i3