[core] Add debugging capabilities

* If an exception is thrown, catch it and show a (somewhat) nice error
  message in the i3bar instead of the normal content
* Add a flag "-d" for debugging into a debug log. Currently, this only
  logs commandline calls as they occur and their return values, as well
  as exceptions.

fixes #58

bumblebee-status

@@ -1,6 +1,8 @@
 #!/usr/bin/env python
 
+import os
 import sys
+import logging
 import bumblebee.theme
 import bumblebee.engine
 import bumblebee.config
@@ -8,17 +10,42 @@ import bumblebee.output
 import bumblebee.input
 
 def main():
+    logging.basicConfig(
+        level=logging.DEBUG,
+        format="[%(asctime)s] %(levelname)-8s %(message)s",
+        filename="{}/debug.log".format(os.path.dirname(os.path.realpath(__file__)))
+    )
     config = bumblebee.config.Config(sys.argv[1:])
     theme = bumblebee.theme.Theme(config.theme())
     output = bumblebee.output.I3BarOutput(theme=theme)
     inp = bumblebee.input.I3BarInput()
-    engine = bumblebee.engine.Engine(
-        config=config,
-        output=output,
-        inp=inp,
-    )
+    engine = None
 
-    engine.run()
+    try:
+        engine = bumblebee.engine.Engine(
+            config=config,
+            output=output,
+            inp=inp,
+        )
+        engine.run()
+    except BaseException as e:
+        logging.exception(e)
+        if output.started():
+            output.flush()
+            output.end()
+        else:
+            output.start()
+        import time
+        while True:
+            output.begin()
+            error = bumblebee.modules.error.Module(engine, config)
+            error.set("exception occurred: {}".format(e))
+            widget = error.widgets()[0]
+            widget.link_module(error)
+            output.draw(widget, error)
+            output.flush()
+            output.end()
+            time.sleep(1)
 #    try:
 #    except KeyboardInterrupt as error:
 #        inp.stop()