More multithreading

Apologies for all the similar screenshots lately;  it’s what happens when I’m working on the behind-the-scenes tech, instead of new features.

So I’ve finally finished converting the world across to being generated in a background thread.  This means that as the player moves around the world, there are no longer any frame rate stutters as new blocks of terrain are created in front of the player.  I’ve also dramatically simplified the world rendering code, which comes as a tremendous relief.

So now that I’m not worrying about performance, I’m going to be diving back into more detailed world-building.  Which should mean more interesting screenshots in the near future!