All public functions could take `impl AsRef<[u8]>` instead of `&str`

[ccptr]

I'm using this crate as a library for a personal tool, and came across this issue when trying to use environment variables as input without validating them to be UTF-8. Now that I'm thinking about it I could just error out if they're not valid UTF-8, but I would still like to be able to do these kinds of things and it is a needless restriction of the API. I'm curious to know your thoughts and/or reasoning behind it.