Add ZIP-244 block commitments as a consensus rule. closes #499
Add ZIP-244 block commitments as a consensus rule. closes #499

It's currently just a note, which makes it look like the Heartwood rule might still apply.

Co-authored-by: teor <7df992f15bda7b1da3fd8c945aef2e4e5b1c226f@riseup.net>
Signed-off-by: Daira Hopwood <cd7d43d5556a38ce626d53826fddc46adc597539@jacaranda.org>

zcash/zips,zcash/zips,zcash/zips,zcash/zips