Basic OO-features in Pipp

When starting on the ReflectionExtension class for Pipp, I got reminded that some very basic OO-features were not working yet. The good think is that I can all that stuff from Rakudo. So simple inheritance and reading member of class instances are working now.

I also simplified my Test.php. The current test number is now tracked in a global variable. Before that change, the test number had to be passed in from the test script.