f18f684ad2 Add version bytes consts (Tobin C. Harding)
Pull request description:
BIP-32 defines 4 4-byte consts used as version bytes; currently we are hardcoding the version bytes in multiple places.
Add BIP-32 version bytes consts and use them throughout the module.
ACKs for top commit:
apoelstra:
ACK f18f684ad2
RCasatta:
utACK f18f684ad2
Tree-SHA512: 50bf2d26f0f8e3528642ffcc621c03b82f536994deb808a6c84225676b4b8849db8e0d16e46f3819e0810296a422b31cf90d0595739910afdb92fb768ef7696e