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.

[raheelsayeed]

Some comments:

1. DateAndTime.swift changes should also apply to the file in fhir-parser-resources, as that's where this file is generated from through the script.
2. Both fhir_isAtEnd and fhir_scanInt no longer need the#if os(Linux) #else since both Linux and Mac implementations are the same.
3. fhir_scanString also may not need if-else due to the above point. It should still use if scanString, though, so the fix is to simply replace NSString with String and then return it without the as String in the current Mac version.
4. Using tabs and not spaces, following convention.