module Caseless:sig..end
Caseless compares and hashes strings ignoring case, so that for example
Caseless.equal "OCaml" "ocaml" and Caseless.("apple" < "Banana") are true, and
Caseless.Map, Caseless.Table lookup and Caseless.Set membership is
case-insensitive.include Comparable.S_binable
include Hashable.S_binable