873501a85f Use slice patterns (Martin Habovstiak)
Pull request description:
Some code looks better with slice patterns. This changes `bip32` to use them.
ACKs for top commit:
apoelstra:
ACK 873501a85f
tcharding:
ACK 873501a85f
Tree-SHA512: 2e91b21d0f943c04f592112f241444ba3b1b1dad47ea6bea162f62cfbcaf98e383257cad144072b3807aaa0c122dabab638ac10b1cc1f5179727a5f05aac0659