Improve boundary between implementation and connection #17
Description
From Matthew's email:
It also seems less that ideal that the Connection class constructs the Calculator implementation internally. Instead, it would be good to construct the Calculator object, then separately start the server loop and pass the implementation object in to the server to call methods on. Right now this is tricky because the Calculator takes an outbound_requester as a parameter, but instead I would suggest that this should be passed as a parameter to the remotely-called method, e.g. you have an additional argument that is a reference to the caller who made the remote invocation, so that you can send messages to the caller if needed. Of course, putting the echo method on the caller and giving both client and server a Calculator implementation is a bit artificial anyway, but I think a reference to the caller would be useful in other situations as well.