code cleanup.
Comments added.
Merge pull request #160 from Asitha/code-cleanup

Code cleanup
Documentation errors fixed
Introducing the path to handle acks received for QOS 1 and 2.
Merge pull request #162 from pamod/mqtt_dev

Introducing the path to handle acks received for QOS 1 and 2.
Merge pull request #161 from Asitha/code-cleanup

Documentation errors fixed