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/button_stop_motion.py

@@ -0,0 +1,12 @@
+from gpiozero import Button
+from picamera import PiCamera
+
+button = Button(2)
+camera = PiCamera()
+
+camera.start_preview()
+frame = 1
+while True:
+    button.wait_for_press()
+    camera.capture('/home/pi/frame%03d.jpg' % frame)
+    frame += 1