Support inheritance

[FGasper]

Inheritance in tests is a much-maligned but occasionally useful pattern.

For example, my team uses a base Test::Class subclass that defines some common “startup” logic. Then any new test script modulino we write that inherits from that base class automatically runs that startup logic.

Is the lack of support for this pattern by design? It would be great if this module were able to be a drop-in replacement for Test::Class, or even just to offer feature parity.

[djerius]

I've implemented a form of inheritance in PR #9