Allow shallow update

Problem

When updating an element, all its children and so forth are checked in order to detect changes. Sometimes we just want to update the whole object.

Also, when updating large objects, dynamo-update-expression will generate a large update expression, resulting in a ValidationException: Invalid UpdateExpression: Expression size has exceeded the maximum allowed size

Proposal

Creating an options object in the update method that determines how that object will be compared and set. We could set a shallow property that doesn't check nested properties and overrides it completely