Feature: volume detection

[daniel-simpson]

Adds code for max and mean volume sensors using ffmpeg's volumedetection argument, as per feature request #74.

There doesn't seem to be any tests in this project (other than linting?), so this is more a proof of concept for now. Very happy to get some feedback if this would be useful, or if I've missed anything.

Thanks!

[irakhlin]

@pvizeli @bdraco what would need to happen to have this work merged? this would be a great addition to https://www.home-assistant.io/integrations/ffmpeg_noise/

[slhad]

I have been looking for volume detection since my son birth, almost 2y, I love your PR @daniel-simpson

[semos2k]

This modification is very useful, is it possible to convert it into a custom component?

[pvizeli]

Can you rebase?

[daniel-simpson]

@pvizeli rebased as requested