#39 way to identify string encodings in midi files

[Chris Cannam]

MIDI files may use any character encoding for their text
events. There are plenty of real examples throughout
Europe using iso-8859-1, for example. But we assume utf8
because that's what we encode everything else in, so
information from any other encoding is lost.

We need a way to guess the right encoding for a MIDI file,
and/or offer the user a choice if non-ASCII text events are
found.