Introduces the IChainableFluentAssert interface and implements it for IStringFluentAssert.
Intermediate step for the refactoring linked to the introduction of the IChainableFluentAssertion interface.
Another step, introducing the IInstanceTypeFluentAssertion<FAT> interface this time.
Restores the InstanceOfType tests for Numbers (in the new chainable assertion model).
Restores the InstanceOfType related to simple object instances.

Thus, introduces a new IObjectFluentAssertion interface.
Restores all the commented tests of the IsInstanceOfTests fixture.

Thus, changes the IEnumerableFluentAssert interface contract.
Finishes the refactoring that introduce the capability to chain assertions (with "And" operator for instance).