add image support: eleventy-img plugin, hero images, responsive picture elements

_includes/column.njk

@@ -14,6 +14,11 @@
   <div class="site-layout">
     <main class="content">
       <article class="column-entry">
+        {% if hero %}
+        <figure class="column-hero">
+          {% heroImage hero, heroAlt or title %}
+        </figure>
+        {% endif %}
         <header class="column-header">
           <h1>{{ title }}</h1>
           <time datetime="{{ date | isoDate }}">{{ date | readableDate }}</time>