[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

tests/test_i3baroutput.py

@@ -0,0 +1,28 @@
+# pylint: disable=C0103,C0111
+import json
+import unittest
+import mock
+try:
+    from StringIO import StringIO
+except ImportError:
+    from io import StringIO
+
+from bumblebee.output import I3BarOutput
+
+class TestI3BarOutput(unittest.TestCase):
+    def setUp(self):
+        self.output = I3BarOutput()
+        self.expectedStart = json.dumps({"version": 1, "click_events": True}) + "[\n"
+        self.expectedStop = "]\n"
+
+    @mock.patch("sys.stdout", new_callable=StringIO)
+    def test_start(self, stdout):
+        self.output.start()
+        self.assertEquals(self.expectedStart, stdout.getvalue())
+
+    @mock.patch("sys.stdout", new_callable=StringIO)
+    def test_stop(self, stdout):
+        self.output.stop()
+        self.assertEquals(self.expectedStop, stdout.getvalue())
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4