Will print debug info to libnotify but additionally print everything to
stdout now.
This should help when explicitly invoking styler from a shell (by
setting `export STYLER_DEBUG=2` or `=3`) and either reading the output
there or redirecting it to a file.
If `send-notify` is recognized as valid command, the dbg_msg function
will send it there instead of printing it to stdout. The urgency of the
message corresponds with low/normal/critical to the debug levels
info/warn/error.
