message: Implement Display for Checksum
diff: use std::convert::TryFrom;
  +use std::fmt;
  use sha2::{Digest, Sha256};
  @@ -19,7 +20,16 @@ impl Checksum {
  /// Creates a lowercase hex encoded copy of this checksum
  pub fn to_hex(&self) -> String {
  - hex::encode(self.0)
  + self.to_string()
  + }
  +}
  +
  +impl fmt::Display for Checksum {
  + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  + for byte in self.0.iter() {
  + write!(f, "{:02x}", byte)?;
  + }
  + Ok(())
  }
  }
  @@ -67,6 +77,22 @@ mod tests {
  assert_eq!(checksum.0, expected);
  }
  + #[test]
  + fn implemented_display() {
  + let wasm = vec![0x68, 0x69, 0x6a];
  + let checksum = Checksum::generate(&wasm);
  + // echo -n "hij" | sha256sum
  + let embedded = format!("Check: {}", checksum);
  + assert_eq!(
  + embedded,
  + "Check: 722c8c993fd75a7627d69ed941344fe2a1423a3e75efd3e6778a142884227104"
  + );
  + assert_eq!(
  + checksum.to_string(),
  + "722c8c993fd75a7627d69ed941344fe2a1423a3e75efd3e6778a142884227104"
  + );
  + }
  +
  #[test]
  fn to_hex_works() {
  let wasm = vec![0x68, 0x69, 0x6a];
  