JDBC 4.2 Support

[enqueue]

The driver should support JDBC 4.2 API, because clients expect driver to work with API as included in Java SE 8.

• Major changes: JDBC 4.2
• Spec: JSR 221 maintenance release 2

This also means dropping support for Java SE 6.

[zhicwu]

@enqueue, I hope it's not too late to get back to this. I'm working on 0.2.5 release which is just about small changes like but fixing and small enhancement. I hope it can be released in mid of Jan, and then if you have time, maybe we can make JDBC 4.2 support as part of 0.3.0 in Feb/Mar?

[zhicwu]

Will fix timezone issue #590 in PR #589.