Add `match` expressions

[slightknack]

Course of action:

• Add match keyword to the lexer
• Add match keyword to the parse tree
• Implement pass to expand match arms into decision trees
• Reduce decicion trees to constructs present in the language core

Here are some papers that might help with the third step. There was this really good gist or issue that explained the algorithm in detail, but I can't seem to find it.

[acorrenson]

Hello 👋

Just a short comment to let you know that there is ongoing work on match statements here ;)

It's going to take a lot of time, but I thought it could be worth mentioning ^^

[slightknack]

Cool! Let me know if you run into any roadblocks that you need me to resolve :)