Test isSupported

kind of stupid, but I don't want to maintain a list of browser UA or
whatever.

src/scripts/lib/is-supported.js

@@ -0,0 +1,8 @@
+module.exports = function() {
+  // Borrowed wholesale from https://github.com/defunkt/jquery-pjax
+  return window.history &&
+    window.history.pushState &&
+    window.history.replaceState &&
+    // pushState isn’t reliable on iOS until 5.
+    !navigator.userAgent.match(/((iPod|iPhone|iPad).+\bOS\s+[1-4]|WebApps\/.+CFNetwork)/)
+}