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/light_sensor_1.py

@@ -0,0 +1,9 @@
+from gpiozero import LightSensor
+
+sensor = LightSensor(18)
+
+while True:
+    sensor.wait_for_light()
+    print("It's light! :)")
+    sensor.wait_for_dark()
+    print("It's dark :(")