dillon1000/react

Use Object.assign in merge/mergeInto

Relax the argument type checks. Currently we throw for non-objects and terminals
but Object.assign does a coercion to Object instead. It also allows merging
Arrays as if they are objects.

This also relaxes the check for dependents such as ImmutableObject. This sucks
but it will allow us to use a fast code path to native Object.assign.

We always have the option of adding warnings to Object.assign or static type
checks.

I'm keeping the null check. Object.assign throws for null checks.

We'll also start returning the result of coercions just like Object.assign.