types and parsers for epoch time and absolute DateTime

I'm guessing that you are calling a specialized method of the form `pow(x: Int, n: Int)`, which obviously returns 0 for n < 0. 

In contrast, what I'm doing will obviously work correctly even with that specialized method. 

Check the docs/source code to verify this is indeed what's happening. But it's not hard to prove that what I'm doing will be correct assuming that `Math.pow(10, n)` works for n >= 0.