Prev/Next arrows are not accessible.

Hey there! I'm just writing to ask about accessibility. Folks who use keyboard navigation do not have an easy way to navigate between the arrows and the slides in a way that makes sense. The arrows come in the DOM after the slide content, when really it should read "Prev arrow, slide content, next arrow" for every instance. Is there a way that we could at least move the previous arrow to be in front of the slide content? Even just that small change would make more sense.

**This generic test case showcases the issue:** https://codepen.io/desandro/pen/azqbop

Start by reproducing the keyboard-navigation behavior in the linked generic CodePen test case, then trace the corresponding carousel markup in Flickity. The work is done when each instance presents the previous arrow before the slide content and the next arrow after it in a logical keyboard reading order.

Written by the indexing model from the issue text.