[core] Disable debugging if "-d" is not specified

Do not print any debugging messages unless "-d" has been specified on
the commandline.
Also, introduce two "special" logfiles "stdout" and "stderr" to log to
stdout and stderr, respectively.

fixes #213

bumblebee-status

@@ -21,16 +21,17 @@ def main():
     config = bumblebee.config.Config(sys.argv[1:])
 
     if config.debug():
+        if config.logfile() in ["stdout", "stderr"]:
             logging.basicConfig(
                 level=logging.DEBUG,
                 format="[%(asctime)s] %(levelname)-8s %(message)s",
-            filename=config.logfile()
+                stream=sys.stdout if config.logfile() == "stdout" else sys.stderr
             )
         else:
             logging.basicConfig(
                 level=logging.DEBUG,
                 format="[%(asctime)s] %(levelname)-8s %(message)s",
-            stream=sys.stderr
+                filename=config.logfile()
             )
 
     theme = bumblebee.theme.Theme(config.theme())