Function from_algo_and_mode_and_digest

fn from_algo_and_mode_and_digest<B: AsRef<[u8]>>(
    algo_and_mode: &str,
    digest: B,
) -> Result<CAHash, Error>

Consume a string containing the algo, and optionally a r: prefix, and a digest (bytes), return a CAHash::Nar or CAHash::Flat.