Accessibility enhancements, creates a figure element with an optional ca...

Full list of changes:

* changed the #holder to a `<figure>` element
* added a little default styling to the table on the example for non-supporting browsers
* made minor, non-impacting changes to the table markup.
* added aria role of `image` on the `<figure>`
* creates a `<figcaption>` if the source table has a `<caption>`
* fakes an ID on `<figcaption>` so that the `<figure>` can reference it with `aria-labelledby`
* added the `<content>` element, so the table can be kept in the DOM, but hidden. This allows screen reader users to access the table
* added summary to the table.

Also adds some project files like .gitignore, etc.