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/led_builtin.py

@@ -0,0 +1,9 @@
+from gpiozero import LED
+from signal import pause
+
+power = LED(35) # /sys/class/leds/led1
+activity = LED(47) # /sys/class/leds/led0
+
+activity.blink()
+power.blink()
+pause()