Refreshed BIP324

The proposal for BIP324, a new bitcoin peer-to-peer (P2P) protocol with opportunistic encryption, bandwidth reduction, and upgradability features has been refreshed. The community members are invited to review the BIP and Bitcoin Core code. The proposal has a rich history, with changes since the last public appearance, including Elligator-swift encoding for pubkeys in ECDH exchange, x-only ECDH secret derivation, transport versioning for upgradability, traffic shapability using decoy packets, and a shapable handshake. The BIP text has also been completely rewritten. Links to the BIP pull request, historical and current PRs, and a gist of the previous appearance are included for review and comments.