[SPARK-11835] Adds a sidebar menu to MLlib's documentation

This PR adds a sidebar menu when browsing the user guide of MLlib. It uses a YAML file to describe the structure of the documentation. It should be trivial to adapt this to the other projects.

![screen shot 2015-11-18 at 4 46 12 pm](https://cloud.githubusercontent.com/assets/7594753/11259591/a55173f4-8e17-11e5-9340-0aed79d66262.png)

Author: Timothy Hunter <timhunter@databricks.com>

Closes #9826 from thunterdb/spark-11835.

2 files changed, 25 insertions, 0 deletions

diff --git a/docs/_includes/nav-left-wrapper-ml.html b/docs/_includes/nav-left-wrapper-ml.html
new file mode 100644
index 0000000000..0103e890cc
--- /dev/null
+++ b/docs/_includes/nav-left-wrapper-ml.html
@@ -0,0 +1,8 @@
+<div class="left-menu-wrapper">
+    <div class="left-menu">
+        <h3>spark.ml package</h3>
+        {% include nav-left.html nav=include.nav-ml %}
+        <h3>spark.mllib package</h3>
+        {% include nav-left.html nav=include.nav-mllib %}
+    </div>
+</div>
\ No newline at end of file
diff --git a/docs/_includes/nav-left.html b/docs/_includes/nav-left.html
new file mode 100644
index 0000000000..73176f4132
--- /dev/null
+++ b/docs/_includes/nav-left.html
@@ -0,0 +1,17 @@
+{% assign navurl = page.url | remove: 'index.html' %}
+<ul>
+{% for item in include.nav %}
+    <li>
+        <a href="{{ item.url }}">
+            {% if navurl contains item.url %}
+                <b>{{ item.text }}</b>
+            {% else %}
+                {{ item.text }}
+            {% endif %}
+        </a>
+    </li>
+    {% if item.subitems and navurl contains item.url %}
+        {% include nav-left.html nav=item.subitems %}
+    {% endif %}
+{% endfor %}
+</ul>