Add clarification about coinbase transaction: it always counts as 0
requested to merge freetrader/bitcoincash-upgrade-specifications:fix/clarify_coinbase_sigchecks_count_as_zero into master
Proposing to add some minor clarification in the SigChecks spec that coinbase txs shall count as 0.
Everyone seems to agree this counting is acceptable as implemented, but the specification was not quite clear on that point.
Also, bump the SigChecks spec out of Draft, to version 1.0.