Deprecate toPublicKey for secretToPublicKey
Deprecate toPublicKey for secretToPublicKey

This is a much better and more explicit naming convention (indeed, I
would have preferred to use `toPublicKey` for `makePublicKey`, but I
think both of them are better off this way.)

Signed-off-by: Austin Seipp <48c905ac3851f382b914247d97dd93273d5ff555@pobox.com>

thoughtpolice/hs-ed25519,thoughtpolice/hs-ed25519