Add an example which shows how to send events out from tasks

Tasks support a notification like channel that they can use
to emit information that has occurred internal to then be
received by any attached listeners. This kind of notification
even works when ran remotely; so this example shows how to use
that system to do something useful.

Part of blueprint more-examples

Change-Id: I104fa55e6b511df77464e3b89ee2bad6438482dd
Merge "Add an example which shows how to send events out from tasks"