unifir 0.2.3

• Bug fixes:
  • Fixed bug where spaces in path to Unity would cause unity_version() and
    create_project() to fail.
  • Fixed InstantiatePrefab C# requirements to now include UnityEditor.
  • Fixed test for new sf and terra versions.
  • associate_coordinates() will now only reproject if both objects have
    coordinate reference systems.
• Documentation changes:
  • Added citation information.