ObjectNode, Message: fixes to properly support class references.
Notifier: added read-only accessor for `@result` instance variable
ObjectNode#invoke: remove obsolete comment about remotely-local references

that is, references to objects that are local for the remote node.
Move message-handling thread introduced in @fd8cc32 to ObjectNode
Implemented new logging system focusing on message flow

Diagnostic messages related to message-passing now use a table-based
--- and color-coded --- format that allows for quickly gaining an
understanding of what ProxyRMI is doing behind the scenes.

While there are (of course!) still improvements that could be made, this
is a great step in the right direction.  As usual, verbose
diagnostics/logging is enabled via the `#verbose=` instance methods.

Warning: uses ANSI terminal escape sequences.
ErrorMessage#exception: fixed; it should work now. ;)
Server#client_loop: use the service-thread `#run()` method

instead of dealing with message-handling ourselves.