Circular Linked List written in rust

Inspired from the linux kernel list.

Basic usage

```rust use cll::CircularList;

let mut mylist = CircularList::default(); for x in 1..=5 { mylist.add(x); }

asserteq!(mylist.remove(), Some(1)); asserteq!(mylist.pop(), Some(5));

mylist.itermut().foreach(|x: &mut i32| *x -= 1); asserteq!(mylist.intoiter().collect::>(), &[1, 2, 3]); ```