A {{ 2col }} shortcode and styling to make a 2 column grid

If the shortcode contains only figures, lay it out wide and add XL margins like
other figures.

layouts/shortcodes/2col.html

@@ -0,0 +1,10 @@
+{{- $size := .Get 0 | default "main" -}}
+
+{{- $classes := slice "two-column" -}}
+{{- if eq $size "wide" -}}
+  {{- $classes = $classes | append "wide" -}}
+{{- end -}}
+
+<div class="{{ delimit $classes "  " }}">
+  {{ .Inner }}
+</div>