Support Quarto's Callout Blocks

[rgaiacs]

Consider

---
title: "MWE"
author: Raniere Silva
---

Foo

::: {.callout-important}

This is important!

:::

We are using quarto render mwe.md --from markdown --to markdown --output mwe.md-output that produces

---
author:
- Raniere Silva
title: MWE
toc-title: Table of contents
---

Foo

<div>

> **Important**
>
> This is important!

</div>

Which is render by Quarto as