When run with the '--autopilot' run option, the 'usb_hid.run' script tests
the input events generated by a 'Pro Micro' microcontroller board. Setup
instructions for the Pro Micro can be found in the run script.
Fixes#2087
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082