Started update to 1.20.

[sclark-dev]

I've ported a fair amount of the code to 1.20. There is still more work to be done, but this is at least a start.

Specifically the Forge code needs to be updated as well as some rendering code. I haven't dealt with either of these in the past so I'm a bit out of my depth. Feel free to either scrap the half-update or use it as a starting point to finish. I'll continue work as I try to figure stuff out.

[Wyn-Price]

Thank you!

This is a pretty good starting point for the port, I can deal with the forge + rendering code at some point. Let me know when you've done all you want to / can, and I can merge this and finish it off.

I've made a 1.20 branch and updated the target branch

[sclark-dev]

As much as I'd like to continue working on it, I have found myself stumped by the new creative tab system. I don't feel particularly confident on trying to bodge a solution.