Add support to Quarto

[rgaiacs]

Quarto is super set of commonmark like MyST.

A minimal working conversion from Quarto to Jupyter Notebook follow the rule already implemented in

plainb/src/parseClassicMd.ts

Lines 4 to 9 in 2585f1c

	// ---------------------------------------------------------------------------
	// Classic markdown parser
	// Two states: MARKDOWN | IN_FENCE
	// Only language-tagged fences (```python, ```js, etc.) become code cells.
	// Untagged fences stay as markdown text.
	// ---------------------------------------------------------------------------

Quarto has support to metadata in the code cells. For example,

```{python}
#| label: fig-polar
#| echo: false
#| fig-cap: "A line plot on a polar axis"
```

For more details, see Code Cells: Jupyter.