ExtendedPubKey and ExtendedPrivKey implemented `ToString` directly but
Rust documentation says to implement `Display` and get the `ToString`
implementation for free.
Signed-off-by: Jean Pierre Dudey <jeandudey@hotmail.com>
Addresses #96.
Turns out it was being used for hex encoding/decoding, so replaced that with the `hex` crate.
i chose to import the `decode` method as:
```
use hex::decode as hex_decode
```
so that it is clear to the reader what is being decoded when it is called. "decode" is such a generic sounding function name that it would get confusing otherwise.
Andrew Poelstra
Carl Dong
Jean Pierre Dudey
Savil Srivastava
Igor Aleksanov
Matt Corallo