The pest book is finally complete now!

https://pest.rs/book/examples/awk.html 🎉

I aimed to keep it in line with the "demonstration of the Rust ecosystem" goal, so it can also be a great introduction to Rust for beginners who are looking for a fun project to work on. It's not perfect, but that's part of the fun! It leaves room for potential language extensions (to make the AWK clone more complete) and optimizations up to the reader as a follow-up.