Simplify image integration

[tdelmas]

In markdown posts, images integrated like that:

[title and alt](/image/exemple.png)

Will generate the html for the image. The image will be centered with the following properties:

• Multiple sizes available depending on the resolution so the UA can select less heavy image
• webp format with a png fallback
• The "title and alt" will be used for alt and title attributes

Images integrated like that:

[title and alt](/image/exemple.png "Some description")

will have in addition a figcaption with that description.

All image are centered.

The magic happen there: https://github.com/letsencrypt/website/pull/1364/files#diff-ca8843b42c6efe94a57c66f9aa842be46241b02bb5db66cd2d6cb6ea5143a012

Advantages:

• Browsers can download optimized/smaller pictures
• less complex html inside Markdown
• Alt text is visible in title, so everybody can benefit from it (not just screen readers). And because it's visible, mistakes can be caught.
• It removes inline css for centering

[tdelmas]

@scottmakestech If you want to take a look

[scottmakestech]

@tdelmas Looks interesting, excited to try this out.