JSON Patch Audit

Judge an RFC 6902 patch against the document it will be applied to. The patch is applied to a copy as a sequence, so each operation is judged against the state it will actually see rather than against the original: a later operation targeting a path an earlier one removed is the defect class this exists for. Reports a missing target, which makes the whole patch fail; a remove, which has no inverse; a replace that changes type; a move into itself; and a path the caller marked protected.