USBHost library in 1.5.1

Hello,

I'm working on making some older code work on the new 1.5.1 USBHost library. I've noticed that the old usb_eventHandler (would be USB_EVENT_HANDLER in the new parlance) does not seem to exist. Was this intentional? The code I'm working on right now requires it (although it's not used for much). I'm happy to submit a patch if it just needs to be added... but if this is intentionally omitted, I'd like to understand why so I can update my stuff accordingly.

Thanks!