Alignment data should be exposed as one of the outputs

[shaunren]

This is useful to determine e.g. the word boundaries in the output waveform.

[orgarten]

I am currently working on this and found the following things:

• The word boundaries are not obtainable, because the sentences are synthesized as a whole
• Synthesizing singular words and accumulating the length (including silent bytes) to get alignment data for individual words is possible but takes much longer and also is anything but accurate.
• Synthesized sentences/words are of different length with each run.

My current implementation would output alignment data for sentences in CSV:

timestamp, word, start_index