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* Add sox_utils module

* Make init/shutdown thread safe

* Add sox effects implementation

* Add test for sox effects

* Update docstrings and add examples

This PR replaces `torchaudio.sox_effects.SoxEffectsChain` in `test_sox_compatibility` with bare `sox` command.

The parity of `torchaudio.sox_effects.SoxEffectsChain` against `sox` command is not tested and it has known issues https://github.com/pytorch/audio/issues/771, therefore it is not appropriate to use this class for testing other functions.

Part of #764

 - Replace `whitenoise.wav` with on-the-fly data generation
 - Replace `torchaudio.load` with `common_utils.load_wav`
 - Replace `steam-train-whistle-daniel_simon.mp3` with `.wav`