Fix sphinx-based search

[vsalvino]

This theme currently breaks the built-in Sphinx search.

The built-in Sphinx search requires the document to have a role="main" attribute (also a good practice for screen readers, etc.) in order to know what content should be searched.

See: https://www.sphinx-doc.org/en/master/templating.html?highlight=role%3D%22main%22#blocks

[Scotchester]

Hmm... I believe the <main> element carries an implied role="main". Shame that Sphinx requires it. We should make sure that it doesn't create an accessibility issue to have both <main> and a descendant with role="main".

[vsalvino]

<article> does permit use of the ARIA role=main (https://developer.mozilla.org/en-US/docs/Web/HTML/Element/article)

But yea, it seems a bit counter intuitive. I would be inclined to replace the <article> element with <main>, since that is actually the real content. The current <main> element has other cruft such as breadcrumbs, edit on github buttons, etc. which are not part of the actual content. The current <main> element should probably be replaced with a general purpose <div>.

There doesn't seem to be any useful guidance on <main> vs <article> 😕

[vsalvino]

@Scotchester at the risk of bike-shedding, I made an alternate layout here... do you think that looks better?

#117