[core/output] Add initial version of i3bar output

Add output handler for i3bar protocol and add some tests for it. Right
now, it only support start and end.

see #23

bumblebee/engine.py

@@ -19,7 +19,8 @@ class Engine(object):
     This class connects input/output, instantiates all
     required modules and drives the "event loop"
     """
-    def __init__(self, config):
+    def __init__(self, config, output=None):
+        self._output = output
         self._running = True
         self._modules = []
         self.load_modules(config.modules())
@@ -45,7 +46,10 @@ class Engine(object):
 
     def run(self):
         """Start the event loop"""
+        self._output.start()
         while self.running():
             pass
 
+        self._output.stop()
+
 # vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4

bumblebee/output.py

@@ -0,0 +1,21 @@
+# pylint: disable=R0201
+
+"""Output classes"""
+
+import sys
+import json
+
+class I3BarOutput(object):
+    """Manage output according to the i3bar protocol"""
+    def __init__(self):
+        pass
+
+    def start(self):
+        """Print start preamble for i3bar protocol"""
+        sys.stdout.write(json.dumps({"version": 1, "click_events": True}) + "[\n")
+
+    def stop(self):
+        """Finish i3bar protocol"""
+        sys.stdout.write("]\n")
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4