This essentially adds support for a derived HDMasterKey to exist.
This follows the coding style guideline that the file that contains a class should follow the exact name of this (main) class. pubkey.{h|cpp} -> PublicKey.{h|cpp} pubkey_utils.{h|cpp} -> PublicKeyUtils.{h|cpp}
Since they are in different libs, it makes sense to put the right part in the right test dir.
tomFlowee