Now the code actually starts to use the Strictness flag that was added in the earlier commit! Well, the *code* doesn’t, but the tests do: the macros that create the test cases now have a parameter for which tests they should run. It’s usually ‘Both’ for both strict mode and default mode, but can be specified to only run in one, for when the results differ (usually when options override one another)
The downside to strict mode is that, now, *any* call to `matches.has` or `matches.get` could fail, because an option could have been specified twice, and this is the place where those are checked for. This makes the code a little less ergonomic in places, but that’s what the ? operator is for. The only place this has really had an effect is in `Classify::deduce`, which used to just return a boolean but can now fail.
In order to more thoroughly test the mode, some of the older parts of the code can now act more strict. For example, `TerminalColours::deduce` will now use the last-given option rather than searching for “colours” before “colors”.
Help and Version continue doing their own thing.
Now it’s more like help. There aren’t any other fields in its struct at the moment, but there will be in the future (listing the features, and extremely colourful vanity mode)
