Have a better way to determine generated outputs version

[NTaylorMullen]

Today we can only use a document snapshots version to differentiate it from other documents. @rynowak had some ideas on how to build a versioning scheme that properly encompasses all the inputs the correspond to a given output.

@rynowak mentioned he'll be working on this so assigning to him.

[NTaylorMullen]

Will need to re-evaluate this once we have a better versioning scheme