Allow for client-specified name for Assertions class

The generated entry-point class is called **Assertions**. If I am using the std **Assertions** class and my generated **Assertions** class in the same test, I can only import one which means the usage of the other has to be fully qualified. It would be nice to be able to add a prefix so that the generated entry-point classes are name **MyProjectAssertsion**, **MyProjectJUnitAssertions**, etc.