[Beta] Text-to-speech pipeline
TorchAudio now adds the Tacotron2 model and pretrained weights.  It is now possible to build a text-to-speech pipeline with existing vocoder implementations like WaveRNN and Griffin-Lim. Building a TTS pipeline requires matching data processing and pretrained weights, which are often non-trivial to users. So TorchAudio introduces a bundle API so that constructing pipelines for specific pretrained weights is easy. The following example illustrates this.
```python



import torchaudio
bundle = torchaudio.pipelines.TACOTRON2_WAVERNN_CHAR_LJSPEECH
Build text processor, Tacotron2 and vocoder (WaveRNN) model
processor = bundle.get_text_processor()
tacotron2 = bundle.get_tacotron2()
Downloading:
100%|███████████████████████████████| 107M/107M [00:01<00:00, 87.9MB/s]
vocoder = bundle.get_vocoder()
Downloading:
100%|███████████████████████████████| 16.7M/16.7M [00:00<00:00, 78.1MB/s]
text = "Hello World!"
Encode text


