leave vs close connections

[joehand]

Closing the connection isn't the same behavior as discovery swarm. I think it might be nice to keep the api consistent, there are use cases where you want to stop announcing but still keep connections open. 'close' or "destroy" can be the thing that kills the connections as well as stops announcing.

We could use close/destroy but would need to have an API for destroing single feed vs the whole swarm.