Added Wait()

This function waits till all the jobs complete but doesn't cleanup
the associated resources. This is helpful in loops where the worker pool needs to be reused and continue the loop only when all the current jobs are completed.

v1.7.0: Added a wait flag in Stop(wait bool) (#15)

* Added a wait flag in Stop(wait bool)
Stop(true) blocks until all the output channels are read from
* Enhanced examples
* start just 1 worker by default to conform to the user input for max workers in case they provide 1