code: func MakeFileBase64Sha512Func(baseDir string) function.Function {
  	return makeFileHashFunction(baseDir, sha512.New, base64.StdEncoding.EncodeToString)
  }
docs: // MakeFileBase64Sha512Func constructs a function that is like Base64Sha512Func but reads the
  // contents of a file rather than hashing a given literal string.