feature: build slide index

templates/slide/slide_index.html

@@ -0,0 +1,9 @@
+<h1>Folien: {{ book["title"] }}</h1>
+<p>{{ book["abstract"] }}</p>
+<div class="chapter-toc d-grid gap-2">
+    {% for chapter in book["chapters"] %}
+        <a class="btn btn-outline-primary btn-labeled" href="{{ book["edition"] }}_slide_{{ chapter["ident"] }}.html">
+            <span class="btn-label">{{loop.index}}</span>{{ chapter["title"]}}
+        </a>
+    {% endfor %}
+</div>