message: document why it is okay to use unwrap in base58::encode
  relates to
diff: @@ -191,7 +191,11 @@ pub mod base58 {
  /// assert_eq!(encoded, base58::encode(decoded));
  /// ```
  pub fn encode(input: &[u8]) -> String {
  - String::from_utf8(base_encode(ALPHABET, input)).unwrap()
  + // unsafe to unwrap the result of `String::from_utf8` as the given
  + // returned bytes are valid within the base58 alphabet (they are all ASCII7)
  + String::from_utf8(
  + base_encode(ALPHABET, input)
  + ).unwrap()
  }
  /// decode from base58 the given input
  