Now waits n=30 secs for any outstanding requests to finish before
giving up and executing a forced shutdown.

Metadata can be used for short replies (less overhead than a full reply)
or to provide information about the reply which will follow (e.g. number
of records, response size, etc.)

Alerts can be used to signal the client about the server state.

Protobufs for different message types will now be handled by template
specialization