Optimization: make the connection GC happy after a UDP loop
UDP fixs and code opts
Set up a bytes pool
Fix a bug that a invalid file-descriptor presents in event-loop
Fix a bug that closes a file-descriptor twice at panjf2000#29
Add new API: conn.Wake() for waking up connection
Renew bytes writing eventFD
Optimize event-loop in handling events
Optimize and structure reactors of epoll and kqueue
Update READMEs