Binary merkle tree implementation with garbage collection support.
```rust use sha2::Sha256; use digest::Digest; use bm::MerkleVec;
type InMemory = bm::InMemoryMerkleDB
let mut db = InMemory::default();
let mut vec = MerkleVec::
for i in 0..100 { vec.push(&mut db, vec![i as u8]); }
vec.drop(&mut db); ```