2.3.0

* Support for GameOverReasonPacket and GameOverStatsPacket (#23)
* Support for DifficultyPacket (#25)
* New properties on BeamFiredPacket (#22)
* Corrected problem with updating red alert and shields status (#20)
* VersionPacket now supports non-float version numbers (e.g. 2.1.1); versions now represented with the Version class (#27)
* Support for NPC surrender
* Unit testing support classes added
* Unit tests for WelcomePacket and VersionPacket added
* Refactor work for man-in-the-middle support (#11; not yet functional)