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.
I'm going to give it a test and it might answer my own question.

Thinking out loud, attr doesn't support type coercion, but clearly it would be nice to have, at least for booleans.