Fast Merkle Trees.

Would define a faster, safer Merkle tree, a way to prove an item is in a list without revealing the whole list.

Bitcoin's original Merkle tree, used to list a block's payments, has a known flaw with duplicate entries and does more hashing than needed. This design avoids the flaw and is about 55% faster to build and check. It is meant for new features, such as BIP 116.