Add initial unit testing logic

[ASpoonPlaysGames]

Doesn't currently use compiler flags or anything but whatever, it works and stuff

closes #707

[uniboi]

Code looks good and works in testing. Unfortunately can't be abstracted further and is a bit fiddly because complex types can never be var
(unless someone writes a plugin)

[ASpoonPlaysGames]

I think that personally I would prefer if unit testing was eventually done via a plugin, but I think that this is a good enough solution for now.

I also don't really see unit testing being used all that much. Most of our functions return void, just doing some work. The option to use unit testing is nice though for some cases

[uniboi]

Yeah unfortunately the actual game is too complex to thoroughly test, just think about entities

[ASpoonPlaysGames]

closes #707