get/setTimestamp should support java.time.Instant

Hi , we plan on making this change in java-driver 4.0 which recently had an alpha release last week. getTimestamp has been replaced with getInstant in java-driver 4.0.

As far as java driver 3.x, we plan on maintaining Java 6 support on that version, but you can use the cassandra-driver-extras module which provides an InstantCodec for working with Instant when dealing with cql timestamp (docs here)

One problem with that is you get ArithmeticException: long overflow for e.g. Instant.MAX.

getInstant works for cql timestamp in 4.0.0-alpha1+