Render figure with shortcode that uses absURL
Ensures that we get the right path to the figure when deploying the site as a subdirectory in the web server root. The filename passed to this shortcode is relative to the Hugo tree's static subdirectory.
This should probably be moved to the site's hugo theme. The shortcode could also include some more options and styling. Deferring for now.
A side affect of using this shortcode is that it seems to work with .svg files, which we had some issues with before. So dropped the .png file.
Part of #54 (closed).