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.

Fix bugs:
 core dump happen in stop_service on restarted service_pump.
 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.

A small optimization for message sending (use message replication rather than parsing message).
Drop direct_broadcast_msg, use broadcast_native_msg instead.

Export some typedefs in container to class queue.

Optimize class queue.

Make client_socket_base be able to call multi_client_base (via i_matrix) like server_socket_base call server_base (via i_server),
 and so does ssl::client_socket_base and udp::socket_base.

Fix statistics for batch message dispatching.
Hide all member variables for developers.

Class object has been split into executor and tracked_executor, object_pool use the former, and ascs::socket use the latter.

Fix: Reconnectiong may happen in ascs::socket::reset, it's not a right behavior.
Do reconnecting in client_socket_base::after_close rather in client_socket_base::on_close.

Support unstripped message.
Add two demos for concurrent test.
define ASIO_NO_DEPRECATED macro by default in VC++ projects.
Truly support asio 1.11 (don't use deprecated functions and classes any more), and of course, asio 1.10 will be supported too.
Use mutable_buffer and const_buffer instead of mutable_buffers_1 and const_buffers_1 if possible.

Support object restoration (on server side).
Re-implement heartbeat function, use user data instead of OOB.
Refactor and optimize ssl object, now ssl::commector_base and ssl::server_socket_base are reuable.

Not compatible with old versions, please note.
See config.h for more details about this release.

Support heartbeat (via OOB data), see ASCS_HEARTBEAT_INTERVAL macro for more details.
Support scatter-gather buffers when receiving messages, this feature needs modification of i_unpacker, you must explicitly define
 ASCS_SCATTERED_RECV_BUFFER macro to open it, this is just for compatibility.
Simplify lock-free mechanism and use std::atomic_flag instead of std::atomic_size_t.
Optimize container insertion (use series of emplace functions instead).
Demo echo_client support alterable number of sending thread (before, it's a hard code 16).
Fix bug: In extreme cases, messages may get starved in receive buffer and will not be dispatched until arrival of next message.
Fix bug: In extreme cases, messages may get starved in send buffer and will not be sent until arrival of next message.
Fix bug: Sometimes, connector_base cannot reconnect to the server after link broken.

known issues:
1. heartbeat mechanism cannot work properly between windows (at least win-10) and Ubuntu (at least Ubuntu-16.04).

Drop unnecessary macro definition (ASIO_HAS_STD_CHRONO).
Simplify header files' dependence.
Add Visual C++ solution and project files (Visuall C++ 14.0).
Monitor time consumptions for message packing and unpacking.
Fix bug: pop_first_pending_send_msg and pop_first_pending_recv_msg cannot work.