Only Propagate Changed Properties

[curran]

The .set method marks all properties passed in as changed, whereas they may not have actually changed.

When used in Redux-style programs, it makes sense to simply pass in all properties. It would be great to be able to use Topologica in this way, and have it "deal with" checking which properties are different than they were before, and only propagating the ones that changed.

The check could be strict equality ===. This would fail in cases where mutated objects are passed in, but I think it's fine to not support this, and say the library only works with immutable property values.