Content in pagination buttons and pause on click.

I added two new options:

- pauseOnclick - A boolean that when `true` pauses the automatic sliding when user clicks in the current visible content. The default value is `false`.

- paginationItem - A function which takes the item index as paramter and returns a string which will fill the button element. The default value is `function( i ) { return ''; }`

I also created [one example](https://gist.github.com/Asakeron/5912947) using both options.

As the default values don't change the current behavior, I believe it's safe to assume this pull request won't cause any compatibility problems.

Thank you.