remove recognized command line options and continue

Gtest's `::testingInitGoogleTest(&argc, argv)` function parses the command line args for googletest flags and removes the recognized ones. Then it continues. This gives me a chance to process my own command line arguments in my library under test.

Can catch2 do something similar? I could hack around this by feeding catch2 a false set of args, but that seems unfortunate when this approach would work much more seamlessly.