nstack

nstack is a stack-like merkle datastructure for storing and accessing indexed values.

Operations supported are add and remove at the end of the structure, and mutable access to indexed leaves.

Usage example

```rust use nstack::annotation::Cardinality; use nstack::NStack;

let mut nt = NStack::::new();

nt.push(0); nt.push(1);

// mutable references to the last element if let Some(mut branch) = nt.nth_mut(1) { *branch = 2; }

asserteq!(nt.pop(), Some(2)); asserteq!(nt.pop(), Some(0)); ```