code: public final Ix<T> repeat(long times, IxBooleanSupplier stopPredicate) {
          return concat(repeatValue(this, times, stopPredicate));
      }
docs: Repeats this sequence if the given predicate returns true after the sequence
  completes in a round or at most the given number of times.
  <p>
  A count of zero will yield an empty sequence, a count of one
  will yield a sequence with only one element and so forth.
  <p>
  The result's iterator() doesn't support remove().
  @param times the number of times to emit the value, non-negative
  @param stopPredicate the predicate called before any emission; returning
  false keeps repeating the value, returning true terminates the sequence
  @return the new Ix instance
  @throws IllegalArgumentException if count is negative
  @throws NullPointerException if stopPredicate is null
  @since 1.0