import { uniqueJustseen } from "https://deno.land/x/itertools@v1.1.1/more-itertools.ts";
Yields elements in order, ignoring serial duplicates.
>>> [...uniqueJustseen('AAAABBBCCDAABBB')]
['A', 'B', 'C', 'D', 'A', 'B']
>>> [...uniqueJustseen('AbBCcAB', s => s.toLowerCase())]
['A', 'b', 'C', 'A', 'B']