Add PWMLED, close #58

gpiozero/output_devices.py

@@ -256,6 +256,10 @@ class PWMOutputDevice(DigitalOutputDevice):
         self._frequency = value
 
 
+class PWMLED(PWMOutputDevice):
+    pass
+
+
 def _led_property(index, doc=None):
     return property(
         lambda self: getattr(self._leds[index], 'value'),
@@ -263,6 +267,7 @@ def _led_property(index, doc=None):
         doc
     )
 
+
 class RGBLED(object):
     """
     Single LED with individually controllable red, green and blue components.