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_2.py

@@ -0,0 +1,20 @@
+from gpiozero import TrafficLights
+from time import sleep
+from signal import pause
+
+lights = TrafficLights(2, 3, 4)
+
+def traffic_light_sequence():
+    while True:
+        yield (0, 0, 1) # green
+        sleep(10)
+        yield (0, 1, 0) # amber
+        sleep(1)
+        yield (1, 0, 0) # red
+        sleep(10)
+        yield (1, 1, 0) # red+amber
+        sleep(1)
+
+lights.source = traffic_light_sequence()
+
+pause()