use bookdown rmarkdown rather than just rmarkdown about binb

[eddelbuettel]

I do not think we should switch to bookdown.

I too have (for specialised sldies) some long yaml headers. But if you look at sister project pinp, its headers are even longer with way more options.

[eddelbuettel]

BTW, multicolumn mode already works. Been doing that for some time.

And you are not using binb so you are filing an issue at the wrong repo. 😀

---
author: Dirk Eddelbuettel
title: Demo
date: 7 Apr 2021
institute: Somehere
output: binb::metropolis
fontsize: 12pt
classoption: compress
---

# Why

## What

### Who

## Simple Example 

:::::: {.columns}
::: {.column width="50%"}

### Left

abc

:::
::: {.column width="50%"}

### Right

def

:::
::::::