a23af7dc31
This adds an `untested` feature to any functions which have not yet been tested live against a YubiKey device (which is presently pretty much everything). This sets a clear expectation of what is presently supported, and additionally documents the status in the README (and a series of GitHub issues). Adds a `cargo build --all-features` to GitHub Actions' `test` step in order to make sure that `untested` functionality still compiles.