Strings Cookbook fixes

* Updated table of contents
* Instaparse grammar was out-of-sync with last-minute change.
* It's not actually a convention to only capitalize a context-free grammar's starting rule. (Conventions like `S` aside.)
* Tell audience that output won't look exactly like `#<byte[] [B@3c3660>`.

(Sorry for the update; I carefully re-checked everything, and will have a better workflow when I release the next cookbook.)