Three Dollar Quill

I tried to put together a signature for the grammar stuff for Earley parsing. I've tweaked it a few times, and I'm almost certainly going to tweak and change it a lot more as I figure out what's actually reasonable and what's needed to actually handle the task of parsing.

I think I have what I need to test it out by actually trying to write the functions, but I'm not up for that right now. We'll see about tomorrow.

Good night.