Add Google Analytics to the docs (#57)

Track user visits so we can get a feel for how many people are using the
docs but anonymize their IPs and disable cookies.

doc/_templates/layout.html

@@ -2,8 +2,18 @@
 {% extends "!layout.html" %}
 
 {% block extrahead %}
- {# Include require.js so that we can use WorldWind #}
- <script src="{{ pathto('_static/require.js', 1) }}"></script>
+ <!-- Google Analytics tracking code -->
+ <script>
+ (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new
+ Date();a=s.createElement(o),
+ m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+ })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
+
+ ga('create', 'UA-38125837-1', 'auto', {'storage': 'none'});
+ ga('set', 'anonymizeIp', true);
+ ga('send', 'pageview');
+ </script>
 {% endblock %}