- Change PoW to KMAC+BLAKE2b-256, remove Cuckoo Cycle.
- Change to a 10 minute block time (updates other constants,
including the halving interval).
- Add `filterRoot` to block header.
- Add a separate witnessRoot.
The last change fixes our original misdesigned segwit, which made syncing a
non-witness chain more difficult than it needed to be. The previous design
merkelized the transaction itself and there was only one merkle root, which was
essentially a witness root. This required "witness data hashes" to be requested
for each block in a non-witness sync. Using a separate tree is just a better
design in the end.
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