Allow posting html for auditing directly

[doug-wade]

I would like to propose an alternative POST body that would be supported in addition to the current POST body.

{
    "name": "my-name",
    "html": "<div>foo</div>",
    "standard": "WCAG2AA"
}

My use case is that I would like to catch a11y issues before they go out, so I would like to write a plugin for the text editor we use on the site (https://www.tiny.cloud/) that posts the contents of the editor on blur, and displays any a11y issues detected as validation errors on the form. This will allow us to alert users of a11y issues when they are authoring their page, and not after it has been released in production.