Aria-hidden attribute incorrectly applied when more than one cell in view

[jasonwbullok]

When more than one cell is visible, only the currently selected cell is exempt from having an aria-hidden: true attribute affixed. This is non-compliant in instances where more than one cell is in view.

The carousel would have to know which cells are inside/outside the viewport to correctly apply the attribute. @desandro called this out explicitly in this thread: #774 (comment)
(which refs issue 638)

Test case: https://codepen.io/jasonwbullok/pen/bGNOrpa
(e.g. inspect cell number two to see the aria-hidden: true attribute)

[desandro]

This is indeed an issue. PR #1032 could resolve this issue.