Advanced HTML output

Option for Windows Explorer-like HTML output - e.g. directory tree on the left, file info on the right. 

Tree would be collapsible. Everything still needs to be contained in one HTML file - e.g. CSS, icons, JS.

Unlike the current HTML output, this should support WAI-ARIA, e.g. https://www.w3.org/TR/wai-aria-practices/#TreeView