No new features, is mostly a cleanup release:
* Methods track_to_events and events_to_tracks methods are removed from everywhere to make place for track_to_tokens and tokens_to_track which make more sens when overridden
* Less redundant code and overridden methods
* token_to_track systematically returns a Instrument object and a list of TempoChange objects which might be the one by defaults when no Tempo tokens are used in an encoding
* Bugfix in Octuple, OctupleMono and MuMIDI: Bar tokens where not created last in the vocabulary dictionary which might lead to mismatching vocabularies when saving and loading back token files
* Updated docstring with some corrections