* Remove explicit host:port parameter from clientRequest
* Save ClientConfig in Client ADT; derive host:port string as needed
* Add Port newtype and endpoint string constructor fn
* Introduce Endpoint newtype for host:port strings; derive them as needed; misc cleanup
* Clean up echo client
* initial echo client/server examples
* registered and unregistered versions of the example client
* ignore pyc files
* cpp echo code, flag to build examples
* threaded server example
