Add support for isochronous transfers

[thegecko]

The specification outlines 2 isochronous transfer methods on a USBDevice; isochronousTransferIn and isochronousTransferOut:

https://wicg.github.io/webusb/#dom-usbdevice-isochronoustransferin

These transfer methods are currently unsupported in node-usb so probably need to be exposed there first.