I assume this breaks the heartbeating and connection deadlining, so I'll try to put a test together for a zero'd heartbeat interval.  How does the client break for you?

The interface was leaning towards `Dial` gives you reasonable defaults for a connection, `DialConfig` gives you complete control over the connection handshake.  0 should be a valid value for a client configured heartbeat interval.

Do you have a suggestion for how clients can indicate they do not want a heartbeat?  The logic is currently encoded in `pick`.