Also extinguishes false positive in typo detection.

Also aims to make corresponding changes to buildinfo-reference-generator, including the `Cabal-described` package. Adds `alphanumNotDigit` and now specifies `alphanum` by inserting digits into `alphanumNotDigit`.

The description of `alpha-num-not-digit` is added to the introduction to the section on 'Non-terminals' to accommodate the limitation of buildinfo-reference-generator that only a single 'formula' can follow a single paragraph of narrative for each non-terminal production.