beIdenticalTo can now be used on non NSObject objects

Taking SwiftHamcrests sameInstance-matcher https://github.com/nschum/SwiftHamcrest/blob/master/Hamcrest/BasicMatchers.swift#L5 this removes the constraint that beIdenticalTo could only be used on objects of classes inheriting from NSObject.
Added tests for beIdenticalTo with objects
Merge pull request #33 from rbeeger/master

beIdenticalTo can now be used on non NSObject objects