2019.4.3.22 - cleaning up the fallout from refactoring

In hindsight, I probably should have done last week's refactoring *before* I started work on the terrain editor, but here we are.

• Fixed bugs upon bugs upon bugs upon bugs
• Made some things look better, particularly the z fighting when you get far away from the terrain, by which I mean I got rid of it
• Tidied up file saving (hopefully this won't be visible to the user though)
• If you're using this for things besides the terrain editor, the last editor mode you will be saved for the next time you open the program, so hopefully that'll save a bit of time

Also, I updated the readme for the first time since about the 8th century.

I'm probably going to stop emphasizing the terrain editor mode next update, since I'm mostly done with that (for now) and I'd really like to get back to the things I was working on before.

With that said, I'll be updating this regularly but I won't post them here unless there's something in it that relates to the terrain editor, since that's what this Itch page is about, or unless I find and kill major program-breaking bugs. If you're interested, follow the repository!