Fixed-sized integers arithmetic
```rust extern crate bigint; use bigint::{U256, Uint};
fn main() { let mut val: U256 = 1023.into(); for _ in 0..200 { val = val * 2.into() } assert_eq!( &format!("{}", val), "1643897619276947051879427220465009342380213662639797070513307648" ); }