Combinable configuration

Allow combining configuration.

For example,

// Fictional example
Tagged("first") + Tagged("second")

should lead to a test tagged with both first and second, not just the last one.

In the same way,

// Fictional example
IgnoredIf { foo() } + IgnoredIf { bar() }

should lead to the test being ignored if both return false.

This could be implemented, for example, by allowing each element to override how it is combined with other elements with the same key.