0.9.4 beta

1. Introduce an outgoing proximity signal. This, if available, will force the outlet proximity pins into a 'disconnected' state (hopefully). That will cause the car(s) to react quicker than the error state.
2. Don't use delay() in error(). Instead, set a time for turning the relay off in the future. If the car reacts more quickly, it will transition to state B and we can turn off the relay faster.