src/test/base-framework.php: Some tidying-up of 'exceptionHandler'.
src/test/base-framework.php: Use __NAMESPACE__ where applicable to make code more portable; refactor mechanism for invoking methods of test-class, to add some type-safety/-hinting.
src/dates.php: Reject non-integer values for parameters ($year and $month) for 'getLastDayOfMonth' function.