Replace with the outline of a simpler scheme. We should be able to
read messages from the wire now, and we will act on messages via a
passed-in instance.
Next is to implement send_version and send_verack; and the receive
equivalents in BitcoinServer. Then we can build a test rig to have
a play.
Once that's tested, we can implement a simple message and start on
the actor - which will be the first non-trivial bit of sharp-coin
proper. We'll be adding features and validations to em-bitcoin &
btc_wire_proto as sharp-coin begin to depend on them for correct
behaviour, and not before.
