mpdstats plugin needs updating to work with python-mpd2 2.0.0

[smcv]

(Sorry, this is just from source code inspection and a search of dependent packages in Debian, rather than a crash that I've genuinely reproduced - I don't currently use beets myself, although I keep meaning to try it.)

https://github.com/Mic92/python-mpd2 version 2.0.0 dropped support for the use_unicode parameter to the MPDClient constructor. This parameter doesn't do anything in Python 3, which always behaves like use_unicode=True. It was important in Python 2.

In Debian's python3-mpd package I've added back compatibility with the use_unicode parameter for now (see Mic92/python-mpd2#142) but I don't know whether that will be accepted upstream.

If beets only supports Python 3, dropping the parameter should be a sufficient fix: replace MPDClient(use_unicode=True) with MPDClient().

If it still supports Python 2, something similar to multani/sonata#116 should work.

[sampsyo]

Thank you for the report, traceback or no! A simple check like in Sonata should do well.