Replace `mp4box` with `mp4-atom`?

Hey @alfg , I was inspired by your library to create [mp4-atom](https://github.com/kixelated/mp4-atom) ([docs](https://docs.rs/mp4-atom/latest/mp4_atom/)) for low-level box encoding/decoding. Would you be open to a PR that uses this library instead of `mp4box`?