Add subcommand that prints the key code for a key on press

[jabcross]

A cursory Google search hasn't shown an easy way to translate scancodes or X keycodes (obtained from xev running under XWayland) to the keycode string that the config expects. I've been tryong to remap the (<>) key (left of Z on my Model M 122) to Super. A simple command that just prints the pressed keycode to stdout until EOF would be very appreciated.

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Edit: Further searching shows that the evtest program already implements this. Leaving this here for anyone searching for the solution in the future, close the issue if you'd like.

The key code was the very descriptive KEY_102ND, if you're curious.