Add isochronous transfer functions and async transfer fill functions. They are implemented directly in Java since they are static inline convenience functions in libusb.h and don't really need to call into C via JNI at all to work, this keeps the JNI layer simple and minimal.
Only fill_control/get_control is still outstanding.
getDescriptor() and getStringDescriptor() were removed from native JNI, since they are static inline convenience functions in libusb.h and don't do anything more than calling the appropriate real function.