Jai grammar for tree-sitter

Very experimental - use the shenanigans branch, as that's where all the action is.

I've only put a couple of days into this so far, and Tree Sitter is anything but intuitive if you've never seen one before. It's even slower going, as I'm trying to add test cases and highlighting cases as I go - so that when I inevitably change something, it doesn't break the world for me.

Compared to the scope of the language, this is not very far along. Based on the size of other Tree Sitter grammars, my estimate would be 50% complete in the best case, more like 25-30% complete.

However, compared to the small subset of the language I currently use, and my general style of coding, it's much further along in terms of what I need - which is nice Neovim highlighting support. I can go to any given how-to or module, and it looks respectable (but clearly incomplete).

I'm not looking to fully define the language, as I think that will take too long. I'm looking for 80%/20% based on my needs. I'll keep chipping away piece-by-piece until I can't particularly see any more progress, and I'm not getting hit with any parse errors in my code.