Add tests

[stackotter]

When I started this project I had no knowledge of Swift and had no idea how to do unit testing. And I'm still a bit lost on the latter. So if you have knowledge of unit testing with Swift please feel free to add a few for a system :)

Systems to test

• [ ] Network stack
• [ ] Mesh building
• [ ] World
• [ ] Config system?
• [ ] I honestly don't really know what sorts of things should be tested so you can add anything else.

Don't feel like you have to do all of those, just choose one or two.

[stackotter]

I have finally gotten around to adding some basic unit tests to Delta Client (already discovered two bugs 👌). I won't be following the list in the original issue description because some of those are pretty complex.