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_1.py

@@ -0,0 +1,9 @@
+from gpiozero import Button
+
+button = Button(2)
+
+while True:
+    if button.is_pressed:
+        print("Button is pressed")
+    else:
+        print("Button is not pressed")