Create a way to update the slides

[imakewebthings]

Folks need a way to update the deck after initialization. I'd like to start with an update or refresh method that rebuilds the internal slide array from the current DOM (using the same slideSelector option from init) and fires an event.

[twitwi]

My pull request #161 only satisfies this partly: it just updates the array and does not apply/unapply the DOM styling etc. It works only when called in the initialization phase (beforeInit).