Enable "n_" JSON tests

[joeslice]

According to https://github.com/nst/JSONTestSuite, test cases whose filename begins with "n_" should result in a parse failure.

These tests were added in #19 but were left skipped to be addressed in this issue.

The scope of this issue is to:

• Clarify parser's behavior in failure mode (messaging, exceptions, etc)
• Enable "n_" tests and make them pass
• For any remaining skipped "n_" tests, file a follow-on issue to address them, or document why they are permanently skippable

[dmarcotte]

The remaining n_ tests to handle are enumerated in JsonTestSuiteEditList. Once those are all eliminated (or documented with why they will be forever-skipped), this can be closed

[dmarcotte]

Done! c8e4b7f