Prevent holding down key from advancing slide

I noticed in use of this code that holding down the arrow or other next/prev keys that the slides would sometimes get into a loop where the hash tag url would keep advancing and the slides would keep updating. (Using the deck.hash.js plugin.) This is easily preventable by setting a timeout on firing the next slide. 100 ms is still fast enough that mashing the key manually advances the slides quickly, but holding it down doesn't advance more than one.