Using AsRef<[u8]> in Arguments

This may have been a conscious choice to avoid but I wanted to see if it makes sense to use some type that implements `AsRef<[u8]>` in place of `&[u8]`? This would make it easy for users to supply `&str` or `String` in addition to `&[u8]` when calling functions. I thought this would be in line with the idea that mundane is intended to be easy to use.

The issue does not name files, tests, or specific functions. Review the library APIs that currently accept &[u8] and determine the scope and compatibility implications of accepting types implementing AsRef<[u8]>. Done means the API direction and affected call sites are clearly decided.

Written by the indexing model from the issue text.