add getSlidePath API method, update URL tests to work with new replaceState throttle

js/reveal.js

@@ -2744,6 +2744,9 @@ export default function( revealElement, options ) {
 		// Helper method, retrieves query string as a key:value map
 		getQueryHash: Util.getQueryHash,
 
+		// Returns the path to the current slide as represented in the URL
+		getSlidePath: location.getHash.bind( location ),
+
 		// Returns reveal.js DOM elements
 		getRevealElement: () => revealElement,
 		getSlidesElement: () => dom.slides,