figures.md: fixes and improvements

Pull Request carpentries/styles#330
Closes carpentries/styles#343

1. Fix the script so that all figures are displayed.
2. Add image numbers.
3. Don't add headers for episodes without images.
4. Add horizontal rulers to better separate adjacent images.
   Don't add a ruler after the last image in the episode.
5. Add empty lines to `figures.md` to improve code readability.
6. Use classes for styling text and figures

Author: maxim-belkin

assets/css/lesson.scss

@@ -163,6 +163,8 @@ article h3 { margin: 40px 0 16px; }
 // Miscellaneous.
 //----------------------------------------
 
+.figures h2 { margin-top: 100px; }
+
 .maintitle {
   text-align: center;
 }

bin/boilerplate/_extras/figures.md

@@ -5,22 +5,49 @@ title: Figures
   window.onload = function() {
     var lesson_episodes = [
     {% for episode in site.episodes %}
-    "{{ episode.url}}"{% unless forloop.last %},{% endunless %}
+    "{{ episode.url }}"{% unless forloop.last %},{% endunless %}
     {% endfor %}
     ];
+
     var xmlHttp = [];  /* Required since we are going to query every episode. */
     for (i=0; i < lesson_episodes.length; i++) {
+
       xmlHttp[i] = new XMLHttpRequest();
       xmlHttp[i].episode = lesson_episodes[i];  /* To enable use this later. */
       xmlHttp[i].onreadystatechange = function() {
+
         if (this.readyState == 4 && this.status == 200) {
-          var article_here = document.getElementById(this.episode);
           var parser = new DOMParser();
           var htmlDoc = parser.parseFromString(this.responseText,"text/html");
           var htmlDocArticle = htmlDoc.getElementsByTagName("article")[0];
-          article_here.appendChild(htmlDocArticle.getElementsByTagName("h1")[0]);
-          for (let image of htmlDocArticle.getElementsByTagName("img")) {
-            article_here.appendChild(image);
+
+          var article_here = document.getElementById(this.episode);
+          var images = htmlDocArticle.getElementsByTagName("img");
+
+          if (images.length > 0) {
+            var h1text = htmlDocArticle.getElementsByTagName("h1")[0].innerHTML;
+
+            var htitle = document.createElement('h2');
+            htitle.innerHTML = h1text;
+            article_here.appendChild(htitle);
+
+            var image_num = 0;
+            for (let image of images) {
+              image_num++;
+
+              var title = document.createElement('p');
+              title.innerHTML = "<strong>Figure " + image_num + ".</strong> " + image.alt;
+              article_here.appendChild(title);
+
+              var img = document.createElement('img');
+              img.src = image.src;
+              article_here.appendChild(img);
+
+              if (image_num < images.length) {
+                var hr = document.createElement('hr');
+                article_here.appendChild(hr);
+              }
+            }
           }
         }
       }
@@ -34,7 +61,7 @@ title: Figures
 Create anchor for each one of the episodes.
 {% endcomment %}
 {% for episode in site.episodes %}
-<article id="{{ episode.url }}"></article>
+<article id="{{ episode.url }}" class="figures"></article>
 {% endfor %}
 
 {% include links.md %}