1. Like a real keyboard, the USB interface descriptor will have an interface
   subclass of boot and an interface protocol of keyboard. This will cause
   some PC BIOS to send a SET PROTOCOL BOOT request to the device.

2. When the device sends reports to the host, if the host requested boot
   protocol, don't send a report ID because boot protocol does not use report
   IDs.

3. To work with some simple PC BIOS:
   a. Use endpoint address of 1 for input and output.
   b. Use separate reports for the shift key. These extra reports can be
      disabled by calling USBHIDKeyboard::setShiftKeyReports(false).