Add `Test.with_clue` function similar to ScalaTest's [with_clue](https://www.scalatest.org/user_guide/using_assertions).
This is useful for tests where the assertion depends on context which is not clear from it's operands.
### Important Notes
Using with_clue changes `State Clue` which is extracted by the `fail` function.
The State is introduced by `Test.specify` when the test is not pending.
There should be no changes to the public API apart form the addition of `Test.with_clue`.
