fixed compile errors on Ubuntu Linux - Swift 4.2

[popaaaandrei]

Foundation libs now unify the signature of scanInt and isAtEnd .

[p2]

That's cool! So for scanInt and isAtEnd, the if-else flags are no longer needed at all, and therefore the whole fhir_* method can be removed?

[popaaaandrei]

Yes, but I need to test it more because the app crashed one time when generating effectiveDateTime. Don’t merge it yet.

[popaaaandrei]

The crash was caused by force unwrapping optionals in DateAndTime parse() method. Apparently on Linux calendar.dateComponents() doesn't return nanosecond component.