Hint for Identity based equals

[jGleitz]

Platform (jvm, jdk8, js, android): jvm

Inspired by #151:

Code related feature

expect(someObject).toBe(anotherObject)

Assuming that both are plain classes and have not overridden equals, we could report that fact with a hint like

» the equals implementation compares object identity

I think it could a helpful hint for a common situation (being that one forgot to implement equals).