The [`lines`](https://docs.rs/ascii/latest/ascii/struct.AsciiStr.html#method.lines) and [`split`](https://docs.rs/ascii/latest/ascii/struct.AsciiStr.html#method.split) methods currently return `impl DoubleEndedIterator<Item = &AsciiStr>`. It would be nice if they returned a concrete type, similar to [`std::str::Lines`](https://doc.rust-lang.org/std/str/struct.Lines.html) and [`std::str::Split`](https://doc.rust-lang.org/std/str/struct.Split.html). A concrete type allows the the iterator to be easily stored in a struct.