message: add some constraints to the AddressLookup trait's associated types
diff: @@ -4,9 +4,9 @@ pub mod randomindex;
  pub mod sequentialindex;
  pub trait AddressLookup {
  - type Error;
  - type AddressInput;
  - type AddressOutput;
  + type Error : ::std::fmt::Debug;
  + type AddressInput : ::std::fmt::Display;
  + type AddressOutput: ::std::fmt::Display;
  /// the implementor will attempt the recognize the given UTxO's credited_address.
  ///
  