Integration with minitest

[dwestheide]

I'd like to see an integration between minitest and Hedgehog. They already have an integration module for ScalaCheck. I am not sure whether a Hedgehog integration should best be a module of minitest or of scala-hedgehog. Given that scala-hedgehog doesn't have proper releases yet, I think that having it in the scala-hedgehog project would work better.

I already implemented the integration. Given minitest's nature, the integration is minimal and requires only a single file with 30-40 lines of code. If there is interest in having this integration in a scala-hedgehog sbt sub project, I will open a PR.

[charleso]

@dwestheide see my comment on #158

[charleso]

(Thanks for reaching out!)