Co-authored-by: Yueh-Shun Li <shamrocklee@posteo.net> `base` is ambiguous, since it's not about the digital bases, but about the format of hashes. Base16, Base32 and Base64 are all character maps for binary encoding. Documentation of the format is also added. Cherry-pick of: https://github.com/NixOS/nix/pull/7708/commits/838c70f62116328ce01cb41a01886e4f1b9a727f https://github.com/NixOS/nix/pull/7708/commits/5043e6cf4ea537dfe599470797c5b310ab0e94b9 Change-Id: Ief5425f3c2056a4cca75838091e4dfa5cca88872