digitallinguistics/spec: v0.16.0

This release adds a new Transcription schema, distinguishing between a Transcription vs. a MultiLangString. The two schemas are essentially the same, but the Transcription schema should be used for data in the target language, whereas the MultiLangString schema should be used for analyses. So the transcription property of a Phrase would be a Transcription object, but the translation property of the Phrase would be a MultiLangString object.