Progress bar builders

Since 0.7.0, apart from standard constructors, you can also use the so-called builder pattern to customize a progress bar.

All setXXX() (also showSpeed) clauses below are optional.

ProgressBarBuilder pbb = ProgressBar.builder()
    .setInitialMax(<initial max>)
    .setStyle(ProgressBarStyle.<style>)
    .setTaskName(<taskName name>)
    .setUnit(<unit name>, <unit size>)
    .setUpdateIntervalMillis(<update interval>)
    .setMaxRenderedLength(<max rendered length in terminal>)
    .showSpeed();
  // or .showSpeed(new DecimalFormat("#.##")) to customize speed display
    .setEtaFunction(state -> ...)
  // This function is of type `ProgressState -> Optional<Duration>` 
  // that should output the estimated ETA of the progress.
  // Returning `Optional.empty()` means that ETA is not available.
for (T x : ProgressBar.wrap(collection, pbb)) {
    ...
}