0.2.0a2

added

• Segment class, attrs-based
  • has asdict method (wrapper around attrs function)
  • has class variable _FIELDS which is used in any place
    where we need to know how to go from Segment attributes to rows of
    a csv file, e.g. in src/crowsetta/csv.py and in tests

changed

• Sequence class is now attrs-based, has factory functions, is itself
  just a list of Segments
  • now has to_dict method
• Crowsetta class is now called Transcriber