corpus-100-* are for general-purpose mixed tests
corpus-1-* are single-item corpori, for running exact-length variations  (made by hand with a clipboard)
corpusx-* are purposed for getting started with the "normalize" test, using randomness to have rare -s, yet awkwardly avoiding SSO with min-length 16
          x means 1% -s

IIRC, ./make-corpus 100 20           DROVE    corpus-100-20-1.txt
ergo, ./make-corpus 100 5 15 0.01    IS FOR   corpusx-100-20-1.txt

./make-corpus 100 5 15 0.01  >  corpusx-100-20-1.txt