Changes -
- in `from_slice` changed the `error` to `FromSliceError`.
- in `verify` changed to `secp256k1::Error` as it can return only one error.
- in `from_str` changed to `FromSliceError`.
- in `CompressedPublicKey` changed `verify` from `Error` to `secp236k1::Error` as it only returns one error.
- introduces CompressedPublicKeyError
- Removes impl from `bip32.rs`
- introduces `ParsePubKeyError` to return errors while generating publickey from string