Merge branch 'master' into when-active-when-inactive

Conflicts:
	gpiozero/devices.py
	gpiozero/input_devices.py

gpiozero/devices.py

@@ -33,6 +33,8 @@ class GPIODevice(object):
 
 
 _GPIO_THREADS = set()
+
+
 def _gpio_threads_shutdown():
     while _GPIO_THREADS:
         for t in _GPIO_THREADS.copy():
@@ -95,4 +97,3 @@ class GPIOQueue(GPIOThread):
             # Parent is dead; time to die!
             pass
 
-