Convert input to join() to unicode

I was getting this error before:

```
  File "/usr/local/lib/python2.7/site-packages/mynt/server.py", line 27, in log_message
    logger.debug('>> [{0}] {1}: {2}'.format(self.log_date_time_string(), self.address_string(), ' '.join(args)))
  TypeError: sequence item 0: expected string or Unicode, int found
````

It turned out that when I got a 404 the error code was sent to `join()` as an int which it can't handle. Hence I added a generator expression to convert all arguments to unicode before passing them to `join()`.