types and parsers for epoch time and absolute DateTime

I guess the question is, do I ever care about the difference between `List(None,None)`, `List(None)` and `List()`?

As a user, do I need to acount for the possibility that you might change the implementation and return `List(DateTime(a), None, DateTime(c))`? 

A somewhat more expressive variation of the current type signature would be:

```
case class DateParseResult(date: Option[DateTime], numNones: Int)
```

This at least encodes the fact that I can get only one `DateTime` out, but this seems like a rather silly return type - I can't imagine where I'd ever use `numNones`.

The speed isn't my concern, that's just a side note. To me this just seems overly complex and underdetermined.