Fix for event listeners being duplicated on source change

docs/src/js/docs.js

@@ -33,6 +33,10 @@ shr.setup({
 		buttons[i].addEventListener('click', newSource);
 	}
 
+	window.addEventListener('popstate', function(event) {
+		console.log(event);
+	});
+
 	function toggleClass(element, className, state) {
         if (element) {
             if (element.classList) {
@@ -113,6 +117,10 @@ shr.setup({
 				break;
 		}
 
+		if (window.history && window.history.pushState) {
+			history.pushState({ 'type': type }, '', '#' + type);
+		}
+
 		for (var x = buttons.length - 1; x >= 0; x--) {
 			toggleClass(buttons[x].parentElement, 'active', false);
 		}