Lazy migrations

[kwando]

Lazy migrations seems like a nice idea =)
Instead of running all migrations once like, do them in a lazily when needed.

https://www.braintreepayments.com/braintrust/data-migrations-for-nosql-with-curator

I can see some potential issues with this though, for instance quering a collection with documents of different versions could potentially be problematic.. but there is cases where it would work properly.