✨ feat: add inline image CSS class

Regular images get a `block` display to be centered.
This allows vertically aligned inline images.

Related: #314

sass/parts/_image.scss

@@ -20,6 +20,11 @@ img {
     height: auto;
 }
 
+img.inline {
+    display: inline;
+    vertical-align: middle;
+}
+
 figure h4 {
     margin: 0;
     margin-bottom: 1em;