Mekle Root FFI

## Build Merkle Root using Rust FFI

**I want Merkly to work like this:**

```py
import merkly

mtree = MerkleTree(['a', 'b', 'c', 'd'], turbo=True)

# build merkle root using Rust by FFI
assert mtree.root.hex() == '68203f90e9d07dc5859259d7536e87a6ba9d345f2552b5b9de2999ddce9ce1bf'
```
