Add multi-level TOC to docs.html

_docs/install.md

@@ -1,6 +1,9 @@
 ---
 toc:
-    install: Install
+    install:
+        _title: Install
+        using-a-pre-bundled-release: Using a pre-bundled released
+        composer: Composer
     run: Run
 ---
 

docs.html

@@ -17,7 +17,18 @@ nav: 2
                 {% for doc in site.docs %}
                     {% for item in doc.toc %}
                         <li>
-                            <a href="#{{ item[0] }}">{{ item[1] }}</a>
+                            {% if item[1]._title %}
+                                <a href="#{{ item[0] }}">{{ item[1]._title }}</a>
+                                <ul>
+                                    {% for sub in item[1] %}
+                                        {% if sub[0] != "_title" %}
+                                            <li><a href="#{{ sub[0] }}">{{ sub[1] }}</a></li>
+                                        {% endif %}
+                                    {% endfor %}
+                                </ul>
+                            {% else %}
+                                <a href="#{{ item[0] }}">{{ item[1] }}</a>
+                            {% endif %}
                         </li>
                     {% endfor %}
                 {% endfor %}