Issue: 51: D-12007: API Checker Error Message Propogation

Added a natural ordering for Result with Result.compare & the Ordered trait
so that the most salient ErrorResult can be selected from a MultiErrorResult.

Priority is dictated by ErrorResult type & then path length in the automaton.

Updated MultiErrorResult to pass all method calls to the most salient ErrorResult
in its PriorityQueue.  Added allResults method which returns a Traversable of
all Results in the MultiErrorResult.

Added test cases to verify priority dictated by ErrorResult and value of
Result.allResults.  Current tests already verify priority by path length.