Create a comparison method

[rasmus91]

Any test suite should have a delegate field, containing a method of comparison of data.

The default method should do the following:

• If the type is a string, int, int64 or uint, comparison should be happening by the == operator
• If the type is a Gee.Hashable comparison should be happening by the .equal_to(...) method
• If the type is neither, compare by reference ( == ) this should generally NOT happen though, as by then, fields within the object will typically be compared instead