Fix bug that changed brightness at each HSV update (#124)

* Fix bug that changed brightness at each hsv update

The HSV setter should accept a percentage for the brightness
value but actually assumed the brightness to be in absolute values
between 1 and 255.
This resulted in brightness reductions at each HSV update, in
steps of 100% -> 100/255=39% -> 39/255=15% -> ... (see also
https://github.com/home-assistant/home-assistant/issues/15582,
where I originally reported this bug).

* Modify HSV property to return brightness in percent

Switch from reported brightness values of 1..255 to percentage
values, for consistency with the apidoc and 8761dd8.

* Add checks and tests for the hsv setter

- make sure that new (hue, saturation, brightness) values are
  within their valid ranges (0..255, 0..100, 0..100) and raise
  SmartDeviceException if they are not
- add test function for the hsv setter

pyHS100/tests/test_bulb.py

@@ -208,6 +208,23 @@ class TestSmartBulb(TestCase):
         with self.assertRaises(ValueError):
             self.bulb.color_temp = 10000
 
+    def test_hsv(self):
+        hue, saturation, brightness = self.bulb.hsv
+        self.assertTrue(0 <= hue <= 255)
+        self.assertTrue(0 <= saturation <= 100)
+        self.assertTrue(0 <= brightness <= 100)
+        for invalid_hue in [-1, 256, 0.5]:
+            with self.assertRaises(SmartDeviceException):
+                self.bulb.hsv = (invalid_hue, 0, 0)
+
+        for invalid_saturation in [-1, 101, 0.5]:
+            with self.assertRaises(SmartDeviceException):
+                self.bulb.hsv = (0, invalid_saturation, 0)
+
+        for invalid_brightness in [-1, 101, 0.5]:
+            with self.assertRaises(SmartDeviceException):
+                self.bulb.hsv = (0, 0, invalid_brightness)
+
 
 class TestSmartBulbLB100(TestSmartBulb):
     SYSINFO = sysinfo_lb100