Move packers and unpackers out of 'include' directory (now in 'ext' directory), they don't belong to st_asio_wrapper library.

Version number not changed.

Force to use c++98 in compatible edition.
Fix bug: if receive buffer overflow and on_msg returns false (which means using receive buffer),
 st_socket will call on_msg again and again (asynchronously) for the same msg until receive buffer becomes available.

Rename temp_object_can to invalid_object_can for better readability, and corresponding access interfaces.
Add validation for some numerable macros
Hide create_object function for server endpoint.

Call on_connect after reset st_connector's status.
Call on_connect before sending and receiving messages.
Avoid changing st_socket ids at runtime.

Changed macro ST_ASIO_SOCKET_FREE_INTERVAL to ST_ASIO_FREE_OBJECT_INTERVAL, ST_ASIO_CLEAR_CLOSED_SOCKET_INTERVAL to
 ST_ASIO_CLEAR_OBJECT_INTERVAL, ST_ASIO_CLOSED_SOCKET_MAX_DURATION to ST_ASIO_OBSOLETED_OBJECT_LIFE_TIME;
Dropped macro ST_ASIO_AUTO_CLEAR_CLOSED_SOCKET, use ST_ASIO_CLEAR_OBJECT_INTERVAL instead;
Changed function st_object_pool::clear_all_closed_object() to st_object_pool::clear_obsoleted_object();
Obsoleted objects' life time will always be zero if ST_ASIO_ENHANCED_STABILITY macro been defined.
st_object_pool support auto close obsoleted objects to release SOCKET handles.
Hide st_object_pool's create_object function for server endpoint.
Simplified st_object_pool and st_ssl_object_pool.
Add a virtual function on_create to st_object_pool.
Add logs for automatically executed tasks in st_object_pool.

Demonstrate how to let st_object_pool to close objects automatically
 (define ST_ASIO_FREE_OBJECT_INTERVAL with ST_ASIO_REUSE_OBJECT).

Fix bug: on Unix alike systems, if server start after client startup, client won't be able to connect to the server.

Fix compiler warnings in asio_server and asio_client.
Fixed the possibility of corrupted sending buffer when link broken.

Move async_call_indicator and related logic from st_timer to st_object.

Fix bug: close st_connector in on_msg or on_msg_handle will cause it reconnect the server even you don't intend to.
Guarantee absolute safety when freeing or reusing st_socket, just need to define ST_ASIO_ENHANCED_STABILITY macro.
Add statistics of idle time on data reception.