New grammar-based parsing system

So I got a little over-zealous and just hacked together a whole new system based on Parslet. It's hopefully much more _readable and maintainable_ (the exact thing all the JSON/YAML/XML/etc. parsers out there _aren't_) and should handle nested arrays, escape sequences in strings, and multi-key keygroups (`[a.b.c]`). Your thoughts?

I'll be pushing some refactorings and such later; just wanted to get your preliminary opinion.