This behavior allow to handle properly the case where an error
(such as a Broken Pipe error) is raised when reading on the socket.
When using SimpleServer class, the socket will be removed from the
connected client list. When using as client, the application is in charge
of re-connection exactly like a desired shutdown. A DEBUG logging message
is emitted by the library when this event is triggered.

RpcError are now reserved to rpc protocol, the RpcConnection uses the new
RpcConnectionError class.

On connection, the new sjRpc work in compatibility mode with the old one. The
label is not defined on frames, and a capabilities special message is sent to the
peer. Old sjRpc ignore this kind on message (but log a warning "malformed
message"), unlike new version which disable this compatibility mode on
receipt.

Now use a callback system to handle event from poller.

When a connection is dropped, all "wait" operations of asynchronous calls
are now released with an error message, exactly like synchronous calls.: