A delay-line buffer for real-time use.
In this example, we mix in a delayed version of the signal `x`, delayed by 2 samples.
```rust
use delay_line::*;
let mut x = [1.0, 0.0, 0.0, 1.0, 0.0, 0.0];
let mut delay = delay_line![0.0; 2];
for x in &mut x
{
}
assert_eq!(x, [1.0, 0.0, 0.5, 1.0, 0.0, 0.5])
```