Modify shutdown to stop all readerWriters
Remove unnecessary mutex

Since using atomic.AddInt32, no need to use Mutex.
Removing code
Saving code for chapter 7 logging
Merge pull request #6 from ssmylh/modify-semaphore-shutdown

Modify shutdown in semaphore.go to work at any number of arguments
Merge pull request #7 from ssmylh/remove-unnecessary-mutex

Remove unnecessary Mutex in chapter6 / patterns / pool / main / main.go
code for io package
Updated example.
Curl example.
saving changes
new example
Updating examples.
added comment
Renamed files to match listing numbers.
Updated code samples and numbers
Updated time code to be more idiomatic.
Updated code samples.
Updated code based on suggestions.
Updated timer code based on suggestions.
Updated code example to be more realistic.