GitLab

Summary:
This commit is kind of clean up and preparation for future
development.

We plan to pass around more complicated objects among
StreamReader and StreamWriter, and TorchBind is not expressive enough
for defining intermediate object, so we use PyBind11 for binding
StreamWriter.

Pull Request resolved: https://github.com/pytorch/audio/pull/3091

Reviewed By: xiaohui-zhang

Differential Revision: D43515714

Pulled By: mthrok

fbshipit-source-id: 9097bb104bbf8c1536a5fab6f87447c08b10a7f2