Add helper function for punctuating a list

e.g. [1,2,3] ⇒ [1, ‘, ‘, 2, ‘, and’, 3]

js/lib/helpers/punctuate.js

@@ -0,0 +1,13 @@
+export default function punctuate(items) {
+  var newItems = [];
+
+  items.forEach((item, i) => {
+    newItems.push(item);
+
+    if (i <= items.length - 2) {
+      newItems.push((items.length > 2 ? ', ' : '')+(i === items.length - 2 ? ' and ' : ''));
+    }
+  });
+
+  return newItems;
+};