In new 2.0 version, just as stated LogWriter is a channel, and a new go-routine 
is spawned to manage the printing.

But when a main program exited too quickly before that go-routine can finish 
processing the logs from channel, then these logs will be lost. Even 
logger.Close() won't resolve this.

Need some extra synchronization codes maybe, like embed a feedback channel 
inside the type LogWriter so logWriter.Close() can exam this channel and wait 
until all logs are printed.