Add switch test example

examples/switch.py

+"""
+switch.py
+=========
+
+Light up all the leds when the USR switch on the pyboard is pressed.
+"""
+
+import pyb
+
+switch = pyb.Switch()
+red_led = pyb.LED(1)
+green_led = pyb.LED(2)
+orange_led = pyb.LED(3)
+blue_led = pyb.LED(4)
+leds = [red_led, green_led, orange_led, blue_led]
+
+while 1:
+    if switch():
+        ## red_led.on()
+        ## green_led.on()
+        ## orange_led.on()
+        ## blue_led.on()
+        [led.on() for led in leds]
+    else:
+        ## red_led.off()
+        ## green_led.off()
+        ## orange_led.off()
+        ## blue_led.off()
+        [led.off() for led in leds]