Add script to convert vits models

[csukuangfj]

Note: We are going to support TTS in sherpa-onnx. The first step is to support vits models.

[csukuangfj]

The following lists some generated waves with this PR.

1

Liliana, our most beautiful and lovely assistant

test-0.mov

2

Ask not what your country can do for you; ask what you can do for your country.

test-1.mov

3

Success is not final, failure is not fatal, it is the courage to continue that counts!

test-2.mov

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Note: GitHub markdown does not support uploading .wav. We use https://www.freeconvert.com/wav-to-mov to convert wav to mov.

[nanaghartey]

unfortunately this does not work when converting coqui tts vits models. Also is there a way to export piper models to generate lexicon and tokens.txt files for mobile?