Modifies the behavior of an update so that it can create an object if it
was new. This allows an "upsert"-like functionality where the SDK will
tend to do the right/expected thing.
This is a tad janky in that it checks for the existence of a class-level
`.create` method which is expected to come from a different module, but
most modules in the project are already fairly deeply intertwined and
co-dependent.
Fixes#165.
ac7d050ecf