Add 97% code coverage CI test.
More test coverage.
Inconsistencies fix:

- getPublicSuffix was not returning its direct host value if found
- getPublicSuffix should not return non-existing suffix values
- getSubdomain was not returning a null value if the domain was unknown
Merge pull request #50 from oncletom/feature-ci-cov

93% to 97% CI code coverage.