Auto slide fragments

This is a small addition to allow users to specify a ```data-autoslide``` attribute for fragments which should fix Issue #650 , Issue #653,  Issue #744  and would be useful for creating a plugin solution for Issue #724.

Example:
```javascript
<section data-autoslide="2000">
	<p>After 2 second the fragment will be shown.</p>
	<p class="fragment" data-autoslide="10000">
As you can hear, the slideshow plays the audio file as soon as the fragment is shown.
	</p>
	<p class="fragment">The next fragment is automatically shown after the previous audio file is played.
	</p>
</section>

```