Add Test Vectors to ZIP 32

[RealityRipple]

trafficstars

Looking to write a server-side HD wallet script in PHP now that z-addrs can be checked for incoming transactions like t-addrs, but without test vectors to verify against, I don't even want to start yet. I was hoping this info would be available before sapling went live, but it's been a few days now and zip-0032.rst still says TBC.

[daira]

Links to the reference code have been added (4a9eb359105d790f6b270b4571c47b5e26d94dd2).