Implement make_refpointer function.

The implementation is akin to std::make_shared and the (to be introduced)
std::make_unique.
Create threadpool attach function.

This function combines the client and service interfaces
and glues them together.  Then it attaches them to both the client
and service.
This allows an N-to-M model of clients and services.
on_client_detach() must be exported, otherwise vtable cannot reference it.
Implement service methods for tp_service_set.
Copyright + sort includes.