Auxiliary elements for collections

Provides well-defined traits with single methods that enable the achievement of maximum flexibility and freedom in several different operations instead of imposing abstract subsets.

```rust use cl_aux::Length;

struct SomeCustomArray([i32; 2], [i32; 4]);

impl Length for SomeCustomArray { fn length(&self) -> usize { self.0.length() + self.1.length() } }

fn main() { let v = SomeCustomArray([1, 2], [3, 4, 5, 6]); assert_eq!(v.length(), 6); } ```

Also provides structures for common use-cases.

```rust use cl_aux::ArrayWrapper;

fn main() { let array: [usize; 1] = ArrayWrapper::fromfn(|idx| idx).0; } ```