Use setuid root instead of adding a sudoers exception

* Thanks to reddit.com/u/Foxboron for pointing out using `install -D` over
  `mkdir` explicitly.

Makefile

@@ -4,7 +4,6 @@ CFLAGS += -Wall -Wextra -O3 -march=native
 prefix = /usr/local
 backlight_dir = /sys/class/backlight/intel_backlight/
 max_brightness = $(shell cat $(backlight_dir)max_brightness)
-backlight_rule = ALL ALL=NOPASSWD: $(prefix)/bin/backlight_control
 
 DEFINES += -D BACKLIGHT_DIR=\"$(backlight_dir)\"
 DEFINES += -D MAX_BRIGHTNESS=$(max_brightness)
@@ -18,9 +17,7 @@ clean:
 	rm -f backlight_control
 
 install: backlight_control
-	mv $< $(DESTDIR)$(prefix)/bin
-	tee $(DESTDIR)/etc/sudoers.d/backlight_control <<< "$(backlight_rule)"
+	install -D -m 4755 -o root -g root $< $(DESTDIR)$(prefix)/bin/$<
 
 uninstall:
 	rm -f $(DESTDIR)$(prefix)/bin/backlight_control
-	rm -f $(DESTDIR)/etc/sudoers.d/backlight_control