More informative FailedCheckError messages

[subsetpark]

Given the highly expressive and nondeterministic nature of property checks, a failed property check can be a little difficult to debug. Ideally there would be help in the modules associated with each property (ie, the ability through the shell h/0 function to obtain a description of the tests associated with each property), as well as messages conveying the test that failed in the property check. Something like

property check `associative` failed for Witchcraft.Semigroup:

from

  a = generate(data) # 1
  b = generate(data) # 200
  c = generate(data) # 6

after 
 
  left = a |> Semigroup.append(b) |> Semigroup.append(c) # 10
  right = Semigroup.append(a, Semigroup.append(b, c)) # 7

we obtained

  equal?(left, right) # false 

Obviously there are many ways you lay it out, but the idea would be to point the developer in the direction of what their generated data looked like and what the relation was that failed.

Would a feature like this be interesting to you, and would you accept any pull requests towards it?