src/ layout, black format, type anno

v1.0.2

v1.0.2

cleanup code, enhance plots, use pytest tmp_file

• cleanup/doc code
• PSD plots instead of spectrogram
• using pytest tmp_file, no problems with writing temp files on CI.

Initial Release

I have been using this to generate background noise for a few years. It works well, so I cleaned it up, pep8, mypy type checking and auto-test on Linux and Windows.

Hope it's useful for you.