HTML to Markdown conversion

[Saladoc]

For previews, like in the Wiki Command, it would be nice to correctly approximate the formatting of the previewed web page. For that we'll need to take the HTML content and properly replicate the formatting in markdown to the best of our ability.

The following formatting elements will be required:

• <strong> to **
• <em> to *
• Headings (likely just treated as bold)
• Weblinks
• <code> both inline and in block form