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/all_on_3.py

@@ -0,0 +1,23 @@
+from gpiozero import LED, Buzzer, Button
+from signal import pause
+
+button = Button(2)
+buzzer = Buzzer(3)
+red = LED(4)
+amber = LED(5)
+green = LED(6)
+
+things = [red, amber, green, buzzer]
+
+def things_on():
+    for thing in things:
+        thing.on()
+
+def things_off():
+    for thing in things:
+        thing.off()
+
+button.when_pressed = things_on
+button.when_released = things_off
+
+pause()