Allow setting float value in slide to show to partially display next slide

Here is a patch to allow float values in the Slides to show field against the 8.x-2.x version.

Thank you.

A good start.

We need to account for any number, not only 1, like seen at asNavFor for this slidesToShow value as said in its description.

3.x is out.

Any betterment should start here, and may or may not be backported.