Fixed issue with UserAttribute events not firing
libVPNET:

- Removed GetUserAttributes(string name) as it is unimplemented
- Fixed TerrainCalculation logic to be accurate, as per extensive testing
- Removed public TerrainCalculation static methods
- Added Point2 struct for TerrainCalculation
- Clarified documentation on Vector3 and StringExt
- Removed ToUnixTimestampUTC (no foreseeable need)

libVPNet Tests:
- Added tests for Instance.Data, utility classes and TerrainCalculation
- Reduced AllUntilTimeout to five seconds
- Better test method naming