feature: allow step matches to be quickly validated

[sdbondi]

Ensuring steps in feature files and in code match is error-prone and requires running the test until it gets to the step, then failing due to a mismatch.

I don't know if there is any way to do this currently, if not, please consider adding it. (Let me know if I can help)

Perhaps something off the top of my head:

  let cucumber_fut = MyWorld::cucumber()
     // Validates that each step matches a defined step. If not, the process exits immediately, reporting which step/s did not match.
      .enable_step_match_validation()
        // ...

I'm not sure if it would be a problem to have this turned on by default, in which case disable_step_match_validation would be more appropriate.