Pub/Sub Subscription's receive method can panic

[SolarLiner]

Right now, using receive and receive_with_options panics on any error (for example, loss of network or socket unexpectedly closed), preventing graceful handling of them. Furthermore, it is impossible to use catch_unwind as the Subscription type is not unwind-safe.

It would make more sense to return a Result and let the library user deal with the handling (or revert to old behavior via .unwrap()/.except()).