[core/engine] Register wheel up/down callbacks for desktop switch

Switch desktop to prev/next on wheel up/down.

see #23

bumblebee/engine.py

@@ -66,6 +66,12 @@ class Engine(object):
         self._modules = []
         self.input = inp
         self.load_modules(config.modules())
+
+        self.input.register_callback(None, bumblebee.input.WHEEL_UP,
+            "i3-msg workspace prev_on_output")
+        self.input.register_callback(None, bumblebee.input.WHEEL_DOWN,
+            "i3-msg workspace next_on_output")
+
         self.input.start()
 
     def load_modules(self, modules):

bumblebee/input.py

@@ -9,6 +9,8 @@ import bumblebee.util
 
 LEFT_MOUSE = 1
 RIGHT_MOUSE = 3
+WHEEL_UP = 4
+WHEEL_DOWN = 5
 
 def read_input(inp):
     """Read i3bar input and execute callbacks"""