Merge pull request #414 from amyangfei/patch

Correct PollItem definitions in Go examples
Fixed comments in examples
Merge pull request #415 from dgrambow/examples

Fixed comments in examples
fix wrong time Duration value in Go examples.
fix wrong return message envelop for mmi.service in Go examples
add examples in Go for Chapter 4. including mmiecho.go and tripping.go
Add three examples in Go for Chapter 3, including peering1/2/3.go