[modules/brighness] Re-enable brightness module

Add a module for reporting, increasing and decreasing the brightness of
a display.

see #23

bumblebee/modules/brightness.py

@@ -0,0 +1,33 @@
+# pylint: disable=C0111,R0903
+
+"""Displays the brightness of a display
+
+Parameters:
+    * brightness.step: The amount of increase/decrease on scroll in % (defaults to 2)
+"""
+
+import bumblebee.input
+import bumblebee.output
+import bumblebee.engine
+
+class Module(bumblebee.engine.Module):
+    def __init__(self, engine, config):
+        super(Module, self).__init__(engine, config,
+            bumblebee.output.Widget(full_text=self.brightness)
+        )
+        self._brightness = 0
+
+        step = self.parameter("step", 2)
+
+        engine.input.register_callback(self, button=bumblebee.input.WHEEL_UP,
+            cmd="xbacklight +{}%".format(step))
+        engine.input.register_callback(self, button=bumblebee.input.WHEEL_DOWN,
+            cmd="xbacklight -{}%".format(step))
+
+    def brightness(self):
+        return "{:03.0f}%".format(self._brightness)
+
+    def update(self, widgets):
+        self._brightness = float(bumblebee.util.execute("xbacklight -get"))
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4