API Clarity: Documented Async Data Broker APIs.

Documented AsyncDataBroker APIs, which are
base abstract APIs from which Binding and DOM
data broker APIs are derived.

Introduced code-examples illustrating
transaction isollation and conflict detection.

Change-Id: I3c881b1fceb0b68c0cc28a1caa7780b9b6c2af3f
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>
Signed-off-by: Devin Avery <devin.avery@brocade.com>
Merge "API Clarity: Documented Async Data Broker APIs."