Introduce macro ST_ASIO_UNPACKER_STRIPPED to control i_unpacker's default value of the stripped property.

Fix the async call indicator (aci) in VC++.

Maintain the ssl::context in ssl::single_client_base.
stop_timer will also invalidate cumulative timers.
Fix warnings in Clang.
Fix ssl graceful shutdown monitoring.

Use header only for Boost.Chrono.
Decouple the id and index for client_socket in file_client.
Fix -- in extreme circumstances, messages can leave behind in the send buffer until the next message sending.
Fix -- basic_buffer doesn't support fixed arrays (just in the constructor) in GCC and Clang.
Introduce macro ST_ASIO_CAN_EMPTY_NOT_SAFE for containers used in send/recv buffer whose empty function is not thread safe.

Add downgrade (to normal UDP) test for reliable UDP in udp_test.

Introduce memory fence to synchronize socket's status -- sending and reading, so use dispatch_strand back in send_msg and recv_msg.

More guarantee on object reusing.
A small refactoring.

Make shutdown thread safe, thus graceful shutdown does not support sync mode anymore.

Fix -- in Windows, a TCP client must explicitly specify a full IP address (not only the port) to connect to.

Fix -- handshake doesn't increase the aci in websocket (include ssl websocket).

Fix type_id conflict (between websocket socket and proxy socket).
Simplify some code for wesocket since it requires c++11.
Tolerate terrible gcc 4.7

Support websocket.
Enhance basic_buffer to support more comprehensive buffers.
heartbeat(ext) optimization.
Add some default implementations for i_matrix interface, which is useful for a dummy matrix.
Fix compilation warnings for Clang.
Fix compilation error with c++17 and higher in GCC and Clang.
Fix alias for tcp and ssl.
Add error check during file reading in file_server/file_client.

Fix bug -- the timer object cannot be used independently because of pure virtual functions.

Fix bug -- if binding local address failed, which means start socket failed, but socket::started() will still return true.

throw more specific exceptions instead of just std::execption.
Enhance basic_buffer -- make it to be able to work as std::string during handling the end '\0' character although with different way.
Optimize memory expansion strategy.
During multi_client_base graceful_shutdown all connections, paramter sync will always be false.

Rollback the support of strict reference balance on multiple io_context, see the release notes for more details,
 so virtual function change_io_context been dropped.
server_base(acceptor) supports the reference customization of io_context.
timer supports the reference customization of io_context, almost all classes inherit from it.
service_pump's single io_context optimization can be closed.

Fix bugs:
 macro ASCS_AVOID_AUTO_STOP_SERVICE will not take effect after service_pump been restarted.
 with macro ASCS_CLEAR_OBJECT_INTERVAL, after stop_service, some sockets can still exist in the valid object queue.
 server_base refuses to start listening if user has opened the acceptor before (to configure the acceptor).
 ssl::single_client_base cannot re-connect to the server.
 server_base's acceptor wrongly takes 2 references on 2 io_contexts.
 Drop function service_pump::get_executor, it introduces above bug implicitly.
 echo_server, echo_client and file_client cannot work after restarted the service_pump.

Make basic_buffer's interfaces more similar to std::string.
Keep the capacity unchanged in basic_buffer::clear as std::string::clear does.
Make basic_buffer copyable.

Support customizing the distribution of multipal io_contexts.
Optimize makefile.

Define macro ST_ASIO_AVOID_AUTO_STOP_SERVICE for demo file_server and file_client as st_asio_wrapper required.

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

Augment certificate's length for demo ssl_test.
Eliminate conflict with windows.h (std::min and std::max).
Demonstrate using non_lock_queue with sync batch msg dispatching.