Check that X12 implementations conform to X12 standard

[kputnam]

Because X12 standards are much easier to understand at a glance (because they omit the element-level details given in an X12 implementation), they could be a good tool to spot-check the definition of an X12 implementation.

There are X12 publications floating around that explain how to define an implementation guide for a given X12 standard. There are some rules like:

• You cannot increase the number of repeats of a loop or segment, but you can lower it
• You cannot add new segments or loops, but you can omit them
• You cannot add new elements to a segment, but you can mark them X: NotUsed
• You cannot change a R: Required element to S: Situational or X: NotUsed
• You can change a O: Optional element to S: Situational or X: NotUsed
• You cannot change the position or ordering of loops or segments
• You cannot add to the set of allowed values in an element, but you can choose a subset

I suspect, even if it's not written explicitly, that any input which can be parsed by an X12 implementation should also be parseable by it's corresponding standard.

Ideally we would implement something similar to Stupidedi::TransactionSets::Validation::Ambiguity to check for conformance in an automated spec. There's no real need to do it at "definition time", since transaction set definitions are static and only change when a new version of stupidedi is released.