Core process manager.
Typo and startup/shutdown tasks.
Rewrite server process architecture.

BaseServer now release on a pluribus.process.Process instance to manage
its threads and tasks centrally.
Clean up imports in the server.
Fix BaseClient to use Process.

BaseClient reworked to depend on pluribus.process.Process for scheduling
and thread and task execution.
Add echo client/server as examples.

No real docs yet, so this is probably more helpful for me than for
anyone else. Working examples of clients and servers using the Process
core.