0.16.0

Breaking changes:

• Drops support for Python 3.6 ahead of its official EOL in December 2021 (#225).
• Tidies up definitions and use of analysis_utils.opt_in() and .responded(), fixing a bug that caused theme_distributions to contain inaccurate NA counts in some cases (#224). This update changed the definitions and call signature of opt_in() and responded().

Other changes:

• Updates Coda data_models to more accurately represent the complete data model used in Coda, and adds new convenience functions:
  • Adds MessagesMetrics (#212, #213).
  • Adds Message.sequence_number (#219).
  • Adds Message.last_updated (#222, #223).
  • Adds Message.get_latest_labels() (#216, #217).
  • Adds Message.copy() (#218).
  • Adds optional serialize_datetimes_to_str=True arg to Message.to_dict() (#226).
  • Adds Label.__eq__() and Origin.__eq__() (#220).
• Adds CleaningUtils.apply_cleaner_to_text (#215).
• Adds swahili.DemographicCleaner.clean_age_within_range() (#228).