Simple type-checking for better merge updates.
Include new fields in diff

RFC: How to handle deleted fields?
Adding simple README to fix NPM errors.
Fix destination object checking when updating after save.
Updating testing and dependencies
Add failing test case for array identity issue

After a successful save, arrays on the instance have the same identity
as that stored as the $original state.

This causes changes to an affected array to occur on the $original state
too, and as a result the changes are ignored in subsequent calls to
$save().