Spotted while navigating https://www.sphinx-doc.org/en/master/.

Trailing whitespace do not have impact on the result, they are just
unused bytes. Most text editors are configured to strip trailing
whitespaces. Remove them all in one go.

Update a handful of files to use the UNIX line ending.

This contained a list of extensions, along with general contributing
information and pointers on how to develop your own extensions. The list
of extensions was very old, referenced the dead BitBucket repo and was
really not very helpful, while the contributing and development
information was just pointers to other, better documentation. Remove the
document wholesale and update any pointers we have to it to other,
better docs.

Signed-off-by: Stephen Finucane <stephen@that.guru>

In HTML5, <script> elements default to MIME type text/javascript. The
HTML5 living standard and MDN recommend against including the attribute.

From https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-type

> The HTML5 specification urges authors to omit the attribute rather
> than provide a redundant MIME type.

From https://html.spec.whatwg.org/#the-script-element

> Authors should omit the type attribute instead of redundantly setting
> it.