Unexpected 'is-animating' pages when turning page right after init

[benjaminlong]

First of all, thank you for your awesome work !

I discovered a tiny bug.
If you programmatically turning a page right after init like this:

var book1 = new Heidelberg($('#Heidelberg-example-1'), {
  previousButton: $('#previous'),
  nextButton: $('#next'),
  hasSpreads: true,
  onPageTurn: function(el, els) {
    console.log('Page turned');
  },
  onSpreadSetup: function(el) {
    console.log('Spread setup');
  }
});

book1.turnPage(5);

Page 5 is active, but webkitTransitionEnd oTransitionEnd msTransitionEnd transitionend events wont be triggered - See file heidelberg.js line 207

els.pagesAnimating.on('webkitTransitionEnd oTransitionEnd msTransitionEnd transitionend', function () {
  els.pagesAnimating.removeClass('is-animating');
  els.pagesActive.removeClass('was-active');
}.bind(document));

and you will have unexpected 'is-animating' pages.

As a result, if you keep turning the pages 'forward', the left page will stay the same.
My goal was to init the book and open it at a given page. I guess, It could be done directly by adding an option to Heidelberg and update the code around line 80-88. But I am not sure it's a wanted behavior.

if(!options.canClose) {
  var coverEl = $('<div />').addClass('Heidelberg-HiddenCover');
  el.prepend(coverEl.clone());
  el.append(coverEl.clone());
  els.pages.eq(0).add(els.pages.eq(1)).addClass('is-active');
}
else {
  els.pages.eq(0).addClass('is-active');
}

I was hoping to come with a pull request to fix this, but I don't have it yet. I was hoping to have some feedbacks and advices from you.

All the best !

[benjaminlong]

Adding an "index" options could result to something like:
benjaminlong@12801e8

[djgrant]

Thanks for the bug report @benjaminlong. I like your solution. Adding an initialActivePage parameter to the options block seems like a sensible idea to me. Feel free to submit a PR for this!