Add “infinite” mode

[tobinibot]

I (and [many](http://stackoverflow.com/questions/15803937/restart-countdown-timer-when-expired other) others) would like timers that automatically reset themselves after expiry. An example use case would just be someone (like me) who wants to update a status page every 30 seconds. Sure, I could just use setInterval, but I like to show a little countdown that displays how long until the page auto-refreshes itself. I could also just restart the timer myself (outside the plugin), but I’d prefer for this functionality to be built in.

I added an infinite option that does just that. If you set infinite to true _and_ you have an until option that is a relative time, then the timer restarts after it expires. If you have an until that is a date, infinite mode doesn’t really make sense, so nothing happens in that case.

Disclaimer - this code works awesome for me, but I have not tested it against all the possible configurations and uses.