Added IgnoreSpec attribute for test methods

Methods inside of a `Spec` class marked with `[IgnoreSpec]` will be skipped. Currently this means that nothing will be listed in the output. Comparing the behavior to [RSpec's Exclusion filters](https://www.relishapp.com/rspec/rspec-core/v/2-5/docs/filtering/exclusion-filters), I'm thinking this is the best way to handle it.

Added a test in `TestSkippingSpec` to verify the behavior. This is done by checking the debug output that the `Verify` call performs and making sure the test method's text is not in there.