revealjs: expose all configuration through attributes (w/ doc)

Also took the liberty to update available configuration parameters up to reveal.js' current master (which is stable).

You might get conflicts with the other pending pull request I made earlier but it'll only be because they both touched the README inserting text at similar locations. `== Settings` should go before `== Example` (to follow deck.js' doc). Sorry about that.
History is nice when designing slides (so you can refresh and be at the right spot) but I find them quite annoying when I view presentations made by others online.

I stuck with upstream's default on this one and when writing content or designing I flip it to true. I could do otherwise.

It's your call but I would prefer sticking with upstream.