Add reliable UDP socket;
service_pump support multiple io_context;
Support connected UDP socket;
Enhance the reusability of st_asio_wrapper's ssl sockets.

Support boost-1.66
Fix race condition when controlling the number of service thread at runtime.
Fix compiler warnings.
Add verification for object allocation.
Add log if stop_timer failed.
Hide variable server in server_socket_base, use get_server function instead.
A boolean value instead of void will be returned from set_timer and update_timer_info.
Move function show_info from server_socket_base and client_socket_base to tcp::show_info.

Rename the name of classes and header files according to ascs, relocate header files according to ascs, macros been kept.
Drop standard edition, use ascs instead.
Support unstripped message.
Truly support asio 1.11.
Optimize send buffer if possible (asio 1.11).
Add two demos for concurrent test.

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