message: add FromStr for Blake2b256
diff: @@ -79,6 +79,12 @@ impl fmt::Display for Blake2b256 {
  impl From<[u8;HASH_SIZE]> for Blake2b256 {
  fn from(bytes: [u8;HASH_SIZE]) -> Self { Blake2b256(bytes) }
  }
  +impl ::std::str::FromStr for Blake2b256 {
  + type Err = Error;
  + fn from_str(s: &str) -> result::Result<Self, Self::Err> {
  + Self::from_hex(s)
  + }
  +}
  impl cbor_event::de::Deserialize for Blake2b256 {
  fn deserialize<'a>(raw: &mut RawCbor<'a>) -> cbor_event::Result<Self> {
  let bytes = raw.bytes()?;
  