Updated swift code to the iOS 6.0.1 new requirements
Added hardware volume buttons handling (both +  and - buttons add +1 repeat now, a preference for handling the buttons in a different way might be added later on)
Fixed a problem of no hardware buttons reaction because of no volume change when it reaches mac/min values by resetting the volume to 0.5 initially and every time it changes; TODO: remember the original volume and set it back it when go to background; use  it or 0.00001 or 0.99999 instead of 0.5