Fixes for issues #6, #7 and #8

Hi, these are the fixes for the above mentioned issues, I'm not sure why I couldn't use the code as the static library, but adding those imports allows me to use it without cocoa pods. There is one more issue that I see which is that the playback will stop if the delegate method returns invalid url, but I'll fix that later. Great lib by the way, the only one I found which allows for a sample precision continuous playback (except AVFoundation but this one freezes when manipulating playback queue, see here: http://stackoverflow.com/questions/16654300/avqueueplayer-playback-freezes-when-removing-items-from-queue)

Cheers!
Jakub