Comparison: The ObjectDifferBuilder now provides new configuration outlet called identity

This allows for providing a custom strategy to establish the identity of collection items base
on something other than the equals method. That's especially useful when you have no control
over the items equals and hashCode methods.

However, it's a brand-new feature and there may be some corner-cases that have not yet been
anticipated. If you run into any trouble using this feature, please feel free to open a ticket
in the issue tracker.

Many thanks to @NagyGa1 for his help on this feature.