Asynmsg

+ Server.get_sessions Server.get_ready_sessions Client.get_ready_session

+ check_session_open,on_session_opened,on_session_closing,on_session_closed
+ Session.get_manage_owner

do not register message handler with duplicate id
fix all classes use the same message map bug

trivial: modify client in example - remove timeout when construct Client

Session.force_close add force_wait_timeout param
add Client.get_session & ClientBlockConnect.get_session
fix Session.handle_write assert error after Session.handle_read get close error

fix README.rst format.