Improve formatting of counterexamples

[emil-e]

Arguments are implemented as tuples and printed as such but this is perhaps an implementation detail that need not be shown. Some other format might be more readable.

Also, for a lot of types, the type itself is not very interesting. Command sequences are a good example, they are vectors of commands but that type is very long and not very interesting.

Some visual cues that show values are picked in sequence?

For a lot of these, it might be useful if you can customize not only the type and the value displaying separately but also change how the value and the type are displayed together.