add addPeriodicTimeObserverForInterval to HysteriaPlayer, it will directly call AVQueuePlayer same method, so it just bring addPeriodicTimeObserverForInterval method to HysteriaPlayer class, also add a current time label to display current time in view controller in example
Merge pull request #53 from chan0123/master

add addPeriodicTimeObserverForInterval to HysteriaPlayer, it will direct...