A note to anyone looking to use this API:

The API is meant to be internal for now, since I have not focused on making it work without using some classes not available in this package.
I would really like to improve this API sometime in the near future, but will be focusing on improving the core of the mod first.
If you find something that's not working you can either write a well-coded Pull Request to fix the problem or let me know that the problem exists.

No guarantees on when I will be working on improving this API myself, but my guess would be sometime during the Summer.

You can use interfaces to check inheritance (e.g. checking if a world provider inherits IGalacticraftWorldProvider to prevent worldgen or something 
similar), but I wouldn't recommend attempting to create your own Galaxies yet.