v0.2.3

Release 0.2.3.

OMX file format has not changed with this release.

Java API changes:

• Performance improvements using 'hyperslabs'

Python API changes:

• Fixed lookup values larger than int16 could hold
• Fixed listAttributes() bug which could result in empty list result
• Lots of tests added, thanks @jiffyclub !
• Code cleanup, thanks @jiffyclub !