Add -b flag for debugging

For now this just prints messages to stderr, so the user should manually
redirect stderr to avoid breaking the ui. This can be later expanded
upon to provide debugging messages in the command window.

Signed-off-by: Loui Chang <louipc.ist@gmail.com>

src/windows.h

@@ -75,6 +75,7 @@ struct arg_opts {
     int ignore_data_file;
     int use_ipv4;
     int force_tcp;
+    int debug;
     int default_locale;
     int use_custom_data;
     int no_connect;