Convert recipe examples to includes

Makes it much easier to test things - no copying'n'pasting just run the
examples straight from the dir (after wiring stuff up)

docs/examples/traffic_lights_3.py

@@ -0,0 +1,24 @@
+from gpiozero import LED
+from time import sleep
+
+red = LED(2)
+amber = LED(3)
+green = LED(4)
+
+green.on()
+amber.off()
+red.off()
+
+while True:
+    sleep(10)
+    green.off()
+    amber.on()
+    sleep(1)
+    amber.off()
+    red.on()
+    sleep(10)
+    amber.on()
+    sleep(1)
+    green.on()
+    amber.off()
+    red.off()