ADD: Markdown.ToHtml from MarkdownDocument

[grishat]

Hello. In my case, I had to add additional classes in html elements. And the best way, in my opinion, was to add attributes on parsed document, and then render this one. And I added this missed method.
Code in my local project:

if (inline is LinkInline link)
{
   link.GetAttributes()
      .AddClass("mud-typography mud-link mud-primary-text mud-link-underline-hover mud-typography-body1");
}