message: add instance ToCBOR for StakeDistribution
diff: @@ -241,7 +241,9 @@ impl StakeDistribution {
  pub fn new_single_key(pubk: &XPub) -> Self {
  StakeDistribution::new_single_stakeholder(StakeholderId::new(pubk))
  }
  - fn cbor_store(&self, buf: &mut Vec<u8>) {
  +}
  +impl cbor::ToCBOR for StakeDistribution {
  + fn encode(&self, buf: &mut Vec<u8>) {
  match self {
  &StakeDistribution::BootstrapEraDistr => hs_cbor::sumtype_start(0, 0, buf),
  &StakeDistribution::SingleKeyDistr(ref si) => {
  @@ -286,7 +288,7 @@ impl Attributes {
  cbor::cbor_bs(v.as_ref(),buf)
  }
  };
  - self.stake_distribution.cbor_store(buf)
  + self.stake_distribution.encode(buf)
  }
  }
  