Add a Bool enum variant for `VehiclePropertyValue`

[aesteve-rh]

          Well, maybe. We would have to add an enum variant and handle the case, ultimately transforming it to int32 when setting the `VehiclePropValue`. I'll open an issue with this dicussion.

Originally posted by @aesteve-rh in #2 (comment)

[aesteve-rh]

cc @barpavel