Refactor/move call sites to functional

[mrufsvold]

This PR moves function ownership up to the JulGame module, refactors UI and Entity to use multiple dispatch, and refactors Camera and the main game loop to use functional call sites.

You'll notice some verbose function calls like JulGame.function(args...). That's not necessary if I import the functions, but before I mess with import/export statements, I just wanted to make sure things were working.

[mrufsvold]

Also, is there a reason that the main game loop has it's own module? It feels like it should belong to JulGame, but I didn't want to mess with your module structure without asking.

[Kyjor]

Also, is there a reason that the main game loop has it's own module? It feels like it should belong to JulGame, but I didn't want to mess with your module structure without asking.

Yeah that's actually something I was planning on working on soon, so if you find it better to do that, please do. I think that's something I did so I could access information from user scripts when I really first started the engine. However you want to change that is fine. The issue that I need corrected (which hopefully this helps you) is that I create an instance of main at the top level.

const MAIN = Main(Float64(1.0))

I believe this is causing the issue with running multiple sessions in the same repl session.

Anyways, take a swing at whatever you wanted to do for that! Thanks!

[mrufsvold]

Cool! I'll take a look at that in a separate PR.