Filtering

There's a single filter right now: based on test names (with a simple `stripos`).

- Filters are no impacted by default test suites or the test suite command line argument. If a user wants to run certain test suites, other command line switches must be used.
- Filters are handled with a new test result status, *filtered*, that's not made accessible from the test context.
- Test cases that are filtered are reported on in the suite summary.