Added some styles using the current-fragment class

according to README, I don't include reveal.min.js.
Hence I believe it makes sense to not include reveal.min.css either.
Hence, examples added in index.html can give the feeling that they don't work yet.

index.html

@@ -302,6 +302,8 @@ function linkify( selector ) {
 						<p class="fragment shrink">shrink</p>
 						<p class="fragment roll-in">roll-in</p>
 						<p class="fragment fade-out">fade-out</p>
+						<p class="fragment current-visible">visible only once</p>
+						<p class="fragment highlight-current-blue">blue only once</p>
 						<p class="fragment highlight-red">highlight-red</p>
 						<p class="fragment highlight-green">highlight-green</p>
 						<p class="fragment highlight-blue">highlight-blue</p>