Lib2P2 handles RPC requests and responses with separate streams
while DEV2P2 is relying on tagged messages transmitted over a
single stream. To cover both models through the same application
code, we introduce a new `response` variable in the request handlers.
The user is supposed to issue a call to `response.send` in order to
reply to the request. Please note that the `response.send` signature
is strongly typed and depends on the current message.