IReadOnlyList<T> for options list

I'd like to suggest list options support more than just `IEnumerable` properties. `IEnumerable` is not a great choice for list properties because it hides information about the underlying collection (order, count).

Adding support for `IReadOnlyList` would be very helpful because it is both ordered (supports an indexer), and has a count. Support for arrays, `ICollection`, `List`, `IList`, `IReadOnlyCollection` are also things that could be considered.