code: function takeNth(coll, nth) {
    if (arguments.length === 1) {
      nth = coll;
      return function(xform) {
        return new TakeNth(nth, xform);
      };
    }
    return seq(coll, takeNth(nth));
  }
docs: Returns a new collection of every nth element of the given
  collection. Returns a transducer if a collection is not provided.