get affix actually working and update docs

docs/assets/js/application.js

@@ -6,11 +6,21 @@
 
   $(function(){
 
+    var $window = $(window)
+
     // Disable certain links in docs
     $('section [href^=#]').click(function (e) {
       e.preventDefault()
     })
 
+    // side bar
+    $('.bs-docs-sidenav').affix({
+      offset: {
+        top: function () { return $window.width() <= 980 ? 290 : 210 }
+      , bottom: 270
+      }
+    })
+
     // make code pretty
     window.prettyPrint && prettyPrint()