This simple plugin does nothing more than provide a `version` focus command,
which will print the firmware version configured at build-time (defaulting to
"0.0.0").
This is a header-only plugin, so that Arduino compiles it in the same
compilation unit as the main sketch, allowing us to set the version from the
sketch, if so desired.
Signed-off-by: Gergely Nagy <algernon@keyboard.io>