Better hashing function

[duckdoom5]

I'm not 100% sure why it happened and I couldn't debug it properly.

When I used the UUID in an unordered map, it would sometimes not find the UUID even though it does exists in the map. I feel like it has something to do with the hash function that this was using.

See this hash_combine proposal for reference to this hashing function: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0814r2.pdf