Pass up annotations in return value from Driver.execute (#760)

* Pass up annotations in return value from Driver.execute
Backward compatible with existing usage.
Adds CircuitState to FirrtlExecutionSuccess, but
that member is not part of the unapply.
"To a single file per module if OneFilePerModule is specified"
test shows example of getting access to annotations

* As experiment return created files in annotations
Fix line missed in last push