add a useful function to convert protocol family to address family.
properly convert protocol family to address family even though they are
same on many platform.
fix the typo.
move socket related functions to KCN library.
rename file names.
follow file name changes.
define LOG_WARN as LOG_WARNING in order to make it shorter.
set SO_REUSEADDR and SO_REUSEPORT on socket.
implement skeletal read/write functions with libevent.
automatically detect libevent.