prosody: place an intonation break at a full stop.
generate_phonemes: output punctiation if needed

This only outputs punctuation when brackets are specified, otherwise
it outputs any associated phonemes with the punctuation event.

This supports two modes:

  1.  assessing the pronunciation of words (e.g. so they can be
      fed to another text-to-speech program, like espeak)

  2.  producing a purely phonetic transcription (i.e. without any
      brackets).