Adding a Symbol.iterator property

[Qix-]

Hey Adam,

would it be possible to add a Symbol.iterator property for better interop?

For example, with SArrays the following fails with a .map() is not iterable error:

const arr = SArray([1, 2, 3, 3, 4, 5]);
const set = new Set(arr.map(i => i > 2));

Thanks!