v3.1.0

Added

• Added model_type option to translate() to use models with higher
  translation quality (available for some language pairs), or better latency.
  Options are 'quality_optimized', 'latency_optimized', and 'prefer_quality_optimized'

• Added the model_type_used field to the translate() response, that
  indicates the translation model used when the model_type option is
  specified.