Add AbortAndRestart example

A small example handler that demonstrates the AbortAndRestart
functionality.

It creates and runs an Async with a payload function that has a 50%
chance to throw an AbortAndRaise Exception or complete successfully.
Add further explanation to abort_and_restart example
Merge branch 'master' into abort_and_restart_example

Conflicts:
	example/__init__.py
Merge pull request #45 from tannermiller-wf/abort_and_restart_example

Add AbortAndRestart example