Added support for registering schema versions. Version bumped to 1.6.0

Fixed long overflow bug in TWO_TO_L calculation for regwidth > 5. Fixes 

aggregateknowledge#10. Version bumped to 1.5.2.

Fix an issue with HLL serialization.

HLL#fromBytes, HLL#toBytes, and HLL#clone weren't taking into account
the Postgres-compatible constructor.

Version bumped to 1.5.0

Fixed aggregateknowledge#4, lowered JDK requirement to 6 from 7. Vers…

…ion bumped to

1.4.0.

Add new HLL constructor. Bump to 1.3.0. Fixes aggregateknowledge#3

- Add an HLL(log2m, regwidth) constructor that defaults to automatic
  EXPLICIT settings and using SPARSE.

Version bump to 1.2.1.

Added artifact signing for Sonnatype.

Version bumped to 1.1.0.