7d1645aea0 Add constant for coinbase maturity (benthecarman)
Pull request description:
Not sure if this is the best place to put this but it is nice to have a constant for this instead of having other libraries make their own (ie https://github.com/lightningdevkit/rust-lightning/pull/1924#pullrequestreview-1222807626)
ACKs for top commit:
tcharding:
ACK 7d1645aea0
apoelstra:
ACK 7d1645aea0
Tree-SHA512: 5ac2a3359cadd303158c66ba45db8f4bf8cc80b6c19604262999ff361fd0bd98e2a4851c57da1962cb5c74f5789a85c8b3861f1742706a60ce1fbc57c3c200cc