Drivers for native USB host port

I am porting the USBH_MIDI library to Due and Zero for my MIDI controller. The Due version works so far. See the following for details.

The Zero version is limping along. It looks like bulk input is blocking for up to 10 seconds waiting for MIDI input. This will require a fix in the Zero USBHost library.

The IDE always recommends updating the USBhost library so I gave it a try. Library manager installed the Due USBHost library. The keyboard example will not even compile so I removed the library. There is a comment in a file that the library is for Due and Zero but it does not work on Zero. BTW, the Due USBHost library works fine on Due. The problem is it conflicts with the built-in Zero library.

I was hoping it would be easy to port the USB host shield drivers. But it has not been easy so far. Has anyone else ported a shield class driver to Due or

I submitted a PR for the 10 second delay. This makes the USB keyboard usable with other devices.