Fixing issue 105 date-time format validation problem

[dezfowler]

Fixing issue #105 which allowed timezone offset to be omitted which is not valid under RFC 3339.

'K' in the format string used will match no timezone.

[JamesNK]

Hi

Thanks for looking at this. I'm going to need to think carefully about this change because it could introduce validation errors to current users when they upgrade. One option could be to include a JsonValidator that validates date-time strictly. Example here - https://www.newtonsoft.com/jsonschema/help/html/CustomJsonValidator.htm

What do you think?

[dezfowler]

Yeah, as highlighted by those broken tests elsewhere in the solution. I kinda left those broken intentionally to highlight this very issue. I was thinking some kind of strict mode would probably be the way forward here.

Given the various drafts of the spec it probably makes sense to have some profiles which just add a particular set of validators.

I've actually identified an additional issue with the date format not covered by my fix and, for my use case, I ideally want to disable the string formats which aren't part of the spec.

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