This modifies the lifecycle of peers to use the more modern Run pattern
that based on contexts.

In particular, this replaces the Start and WaitForDisconnect methods
with a single method named Run and arranges for it to block until the
provided context is cancelled or the peer is disconnected.  This is more
flexible for the caller since it can easily turn blocking code into
async code while the reverse is not true.

The new Run method waits for all goroutines that it starts to shutdown
before returning to help ensure an orderly shutdown.

Since all exported methods that send messages to the various groroutines
via channels already select across the quit channel which is closed when
the peer disconnects, the peer is now forcibly disconnected when the
context is cancelled.

This approach allows the flexibility for callers to use any combination
of manually disconnecting peers via the Disconnect method and allowing
them to automatically be disconnected when the context is cancelled.

It also updates the server code accordingly.