feat: use anyhow

[Odilf]

Closes #24

Change the hand rolled Box<dyn Error> approach for error handling to simply using anyhow.

This is a breaking change if someone uses errors. However, the migration should be fairly straightforward:

1. Change ffmpeg_sidecar::error::Result to anyhow::Result
2. Change ffmpeg_sidecar::error::Error to anyhow::Error

If someone is using Error directly (i.e., getting the message or the source) then they should consult the anyhow docs to find the equivalent functionality for their use case.

[nathanbabcock]

Great job with this PR. CI passes, all examples work, and the code changes are minimal.

I also appreciate how utilities in anyhow make the source code cleaner, things like anyhow::bail!(...) instead of return Err(Error::msg(...)), and .context(...) instead of .ok_or_else(|| ...).

I will merge this and plan to publish a release on Cargo next week. Since this is technically a (small) breaking change, I'll bump the major version number. Coincidentally, next week will be one year since the first released version, v0.1 in Feb 2023.