Connection aware handlers - more messaging less request-reply

[codingchili]

Add a new interface, ListenerAware or add default methods to CoreHandler

• onConnect(Client client)
• onDisconnect(Client client)

Clustered session management could be set up in these methods.

Other changes

• interface Client implements MessageOperations, which is to be renamed.
• MessageOperations::write returns a Future to signal success. Fails if the connection is closed.
• Add client() to requests (or extend client interface). A request is a client + some request data. request.client() must match any clients passed through listener methods.

Facilitates the following

58

190

Delimitations

• ClusterListener does not have to keep track of clients between requests.
• RestListener does not have to keep track of clients between requests.

[codingchili]

Requests now provides a Connection object, on which handlers can be added for the onClose event. Transports that does not support persistent connections may throw an exception, or use the volatile request context.

Uses of the UDP transport are encouraged to implement timeouts.