added Google Analytics to the documentation site

Author: musketyr

docs/docinfo.html

@@ -1 +1,11 @@
-<link rel="stylesheet" href="css/spreadsheet-builder.css?v={version}" />
+<link rel="stylesheet" href="css/spreadsheet-builder.css?v={version}" />
+<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','//www.google-analytics.com/analytics.js','ga');
+
+    ga('create', 'UA-68778580-1', 'auto');
+    ga('send', 'pageview');
+
+</script>