Classic English readability metrics with no dependencies

Flesch reading ease, Flesch-Kincaid grade, Gunning fog, SMOG, Coleman-Liau, the automated readability index, LIX and RIX, computed from a single tokenising pass over the text. Includes the sentence, word and syllable counters the formulas are built on, so they can be used and tested on their own, plus a readability command line tool that prints a table or a JSON object. Depends on nothing outside the OCaml standard library.