Update push.js

added PUSH function to global scope so it can be triggered from JS

PUSH({
  url: 'foo.html',
  transition: 'slide-in'
});

lib/js/push.js

@@ -414,5 +414,6 @@
   window.addEventListener('touchend', touchend);
   window.addEventListener('click', function (e) { if (getTarget(e)) e.preventDefault(); });
   window.addEventListener('popstate', popstate);
+  window.PUSH = PUSH;
 
 }();