Kramdown's refdef used incorrectly

[soup-bowl]

refdef is used throughout for apply a class to center images. This appears to be wrong, as it's for applying generalised styles and not for the current use case.

Switch:

{:refdef: class="article-image"}
![Example Image](example.png)
{: refdef}

to:

![Example Image](example.png)
{: .article-image }