Adding custom assertions to MSTest

Even though MSTest does not provide the same extensibility capabilities as NUnit, it is still possible to add these missing Assert methods by creating your own class library to reference in your unit test project. In order to help ease any potential issues in migrating from NUnit to MSTest caused by the lack of these Assert methods, I have created a class library that includes all of them except the FileAssert methods and StringAssert.IsMatch. These methods should behave exactly like they do in NUnit. (In fact, the unit tests are the same ones used in NUnit, with only a few minor differences.)