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/motor.py

@@ -0,0 +1,10 @@
+from gpiozero import Motor
+from time import sleep
+
+motor = Motor(forward=4, backward=14)
+
+while True:
+    motor.forward()
+    sleep(5)
+    motor.backward()
+    sleep(5)