Implement behavior to clean up numeric suffixes in exercise directories

[kytrinyx]

When we launched the v2 site, the CLI had some funky behavior that sometimes adds a numeric suffix to the exercise directory. This behavior is going away.

The exercism doctor command should clean any of these up.

We can rely on the workspace.PotentialExercises() functionality to do this, and then group them into each group of related exercises. E.g.

• ruby/hello-world
• ruby/hello-world-2
• ruby/hello-world-3

These would all be in one group.

For each group where there are any exercises with a suffix we should have an interactive prompt. Something like:

Which one would you like to keep? Select your choice by typing the number.
1. hello-world
2. hello-world-2
3. hello-world-3
4. Skip this one. Do nothing and move on.

If they select one of the exercises (not skip), then:

• delete all but the selected one
• rename the selected one to remove the suffix (if it has one)

Additional error handling

In the download command we should bail with an error if trying to download to an exercise directory with a numeric suffix.

In the submit command we should bail with an error if trying to submit an exercise that is in a directory with a numeric suffix.

The error messages should suggest running exercism doctor.