Bitcoin Cash: Support aserti3-2d DAA

[jonas-lundqvist]

On November 15 there will be a planned network upgrade on the Bitcoin Cash network that will activate a new and non backwards compatible Difficulty Adjustment Algorithm called aserti3-2d. Breadwallet needs to implement it since the wallet is verifying the block headers and thus verifying the difficulty.

Specifications can be found here:
https://www.bitcoincash.org/spec/2020-11-15-upgrade.html
https://upgradespecs.bitcoincashnode.org/2020-11-15-upgrade/

Please note that there will also be an additional soft-fork as specified in the "Coinbase Rule" by Bitcoin ABC and most certainly a chain split since no other full node software is implementing it. Not implementing the soft-fork will let the wallet follow the chain with most Proof-of-Work.

[imaginaryusername]

example bitcoincashj implementation: https://github.com/pokkst/asert-java