Introduce spreewald binary that lists all Spreewald steps

When writing Cucumber features I was regularly opening Github, browsing to the steps directory and searching for a step I could make use of. That's tiring.

Now Spreewald offers a binary that will list all steps, sorted. It's great for quickly checking which steps are available, and you can easily grep that list: `spreewald list | grep see`.

I felt Spreewald could be released as 1.0, since it has been around for a while and is feature-complete (pun intended).